Change any Colour Using the Affinity Photo Colour Replacement Brush

by Feb 9, 2022Photo Editing Tutorials

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Change Any Colour Using the Affinity Photo Colour Replacement Brush

In this tutorial, we use the Affinity Photo Colour Replacement Brush to change the colour of a boat from red to green. This is a great tool for changing the colour of any object, but it does have some limitations as you will learn in this tutorial.

An alternative to the Affinity Photo Colour Replacement Brush is the HSL Adjustment which can be used to replace the colours in an image.

Here’s the photo we will be using, showing a red boat.

example image showing the red boad which will have it's colour repalced

What’s great about the Affinity Photo Colour Replacement brush is that it replaces the colours in objects  like this boat so well that you don’t realise the colour has been changed. It’s also extremely easy to use once you understand how it’s working.

How the Affinity Photo Colour Replacement Brush Works

The Colour Replacement Brush Tool works by selectively replacing colours with another colour as you paint. It does this by sampling the colour in an area of the image where you paint and then replacing it with a different colour you have selected.

In the example of the red boat, we can tell Affinity Photo to replace the colour red with green. Then when we paint over something that’s red with the Colour Replacement Brush, it changes it to green.

red of boat replaced by green using the color replacement brush tool in affinity photo

This gives you total control over where the colours are replaced in an image. If you look at the photo above, you would never realise that the boat wasn’t green. Look more closely around the image and you will see other areas of red that are untouched by the change. This is the power of the Colour Replacement Brush tool.

Selecting the Colour Replacement Brush Tool

The Colour Replacement Brush Tool is in the Affinity Photo Tools Palette on the left of the interface.

The brush is part of a larger group of tools which includes the Paint Brush Tool and the Pixel Tool. It’s possible one of these other icons is displayed in the Tools Palette. If it is, click and hold down your mouse button on that icon. This expands the group to display all the tools, allowing you to select the Colour Replacement Brush.

Selecting the Colour Replacement Brush Tool in the Affinity Photo Tools Palette

After selecting the Colour Replacement Brush, you need to configure it before you try to use it. The first step is to select the replacement colour.

Selecting the Replacement Colour

The replacement colour is the new colour we want to apply to the boat in our example.

The easiest place to set this is probably in the Swatches Studio Panel but you can also use the Colour Studio Panel if you prefer. These panels may be located on the right of your interface, but it depends how you have Affinity Photo laid out.

If you can’t see the studio panel, check that it’s visible using the Affinity Photo View menu. You can do this by selecting the View menu and then the Studio option to see a list of Studio Panels. The panels with tick marks next to them are the ones that are visible. Click on the Swatches option in the menu to toggle its visibility off and on. This is probably sufficient for you to see the panels’ location.

You can see an example of the Swatches Studio Panel below.

Affinity Photo Swatches Studio Panel

At the top of the Swatches Studio Panel, you will see the current foreground and background colours (number 1). It’s the foreground colour that the Colour Replacement Brush uses to replace another colour in the image.

You can pick a new foreground colour to use by clicking a swatch. You can also switch between the foreground and background colours by clicking the small, curved arrow to the top right of the two discs, or by pressing X on your keyboard.

It’s quite possible your Swatches panel looks different to the screenshot above. You can change between different panel views by clicking the dropdown list (number 2). The dropdown list setting in the screenshot is “Colours”.

After selecting the replacement colour, we can begin to change colours using the Colour Replacement Brush.

Replacing a Colour with the Colour Replacement Brush

After setting a replacement colour, if we move the mouse pointer over the red boat, the Colour Replacement Brush displays a preview of the new colour. You can see an example of this below.

example colour replacement brush preview

If we then click with our mouse, the colour is replaced in that area of the boat. Then if we continue to hold down the mouse button and paint with the brush, the colour is replaced everywhere that we paint. This is how simple it is to use the Colour Replacement Brush, but there is a little more to understand to achieve the best results.

The Colour Replacement Brush is a Destructive Edit

It’s important to understand that the Colour Replacement Brush is a destructive editing tool. This means it directly affects the pixels of the image layer. It’s therefore a good idea not to paint directly onto the background image layer, but rather use a duplicate image layer.

You can duplicate the image layer in the Layers Studio Panel by right clicking on the image layer. This displays a popup menu where you can select the “Duplicate” option. You will then see the new duplicate image layer appears in the Layers Studio Panel.

If your image has multiple layers rather than a single background layer, you can create a new Stamp Layer. A Stamp Layer consolidates all the visible layers in an image into a single new layer. You can create this using the keyboard shortcut Shift + Option + Cmd + E on a Mac. Or ff you’re using a PC it’s Shift + Ctrl + Alt + E.

Now be sure to select the new image layer, which should be at the top of the Layers Studio Panel. You can then click on the colour you want to replace in the image and paint with the Colour Replacement Brush.

Colour Replacement in progress

Whilst the Colour Replacement Brush seems to almost magically replace the colour in the image with a new colour, you might see some problems.

Notice in the screenshot above that I’ve spilled over into the water on the left side of the boat. Ideally you should keep as close to the edge of the object as possible without allowing the centre of the brush to move outside the area. You’ll learn why shortly.

If you spot a problem like the one above when painting, it’s best to undo and repeat the brush stroke. But if you miss the mistake, you may be able to fix it later using a mask.

The Sample Continuously Option

In the example above the colour replacement has spilled over into the water. There are also other difficult areas where this could happen like where you see the reflection of the red of the boat on the water. One way to avoid this is by changing the Sample Continuously option for the brush.

You’ll find the Sample Continuously option in the Affinity Photo Context Sensitive Toolbar, at the top of the interface.

Sample continiously option for the colour replacement brush tool

This instructs the Colour Replacement Brush to continuously sample the colours within the brush as you paint. It does this using a small central area of the brush. It then replaces the sampled colour within the circumference of the brush with the new replacement colour you selected.

If we try to paint over an area like the water where the red of the boat is reflected, it’s likely that the brush will sample the water as we paint. This is why the water turns green and not just the red reflection.

By unchecking the Sample Continuously option, the sample is taken when you first click to start painting with the brush. The Colour Replacement Brush then continues to use this colour sample until you release the mouse button. This allows you to sample the red of the boat by clicking on it and then paint over the reflection in the water, without affecting the surrounding water. You can continue to do this until you release the mouse button.

Changing the Colour Replacement Brush Tolerance

When painting over small areas like the reflection in this image, it can help to magnify the area. This allows you to work with greater precision as well as size your brush to fit the area you want to change.

When you paint over the red reflection you may find that you are still affecting the blue of the water. This can happen if the Tolerance setting of the brush is too high. By reducing the Tolerance setting you can prevent the brush from replacing the blue colour of the water whilst allowing it to accurately replace the red.

replacing the colour of the red reflection on the water

Here you can see what happens when the Tolerance is reduced to 10%. This shows that the red reflection is replaced without affecting the blue water.

When you use a high Tolerance setting, you replace a wider range of colours with the brush. Using a lower Tolerance allows you to replace a narrower range of colours, making the brush more accurate. The brush preview allows you to check its effect before painting and adjust the Tolerance if necessary.

red reflection replaced with gree

By painting carefully at full magnification and using the controls mentioned, it’s possible to replace the red of the boat completely with green. You would never know that the boat in the photo wasn’t green.

red of boat replaced by green using the color replacement brush tool in affinity photo

Now let’s look at how to clean up the mistake I made earlier when I painted over the water next to the boat.

Cleaning up the Colour Replacement Layer with a Mask

Earlier I said it was possible to clean up colour replacement mistakes with a mask. Ordinarily it’s better to correct these using the Undo option before continuing to paint. Sometimes though, you don’t notice a problem until later, which is when you can use a mask to fix it.

To do this, select the layer you’ve been working on in the Layers Studio Panel. You can then click on the icon to the bottom of the panel to add a mask layer (number 1 below).

adding a new mask layer to clean up the colour replacement layer

Clicking the icon adds a new mask layer to the selected layer (number 2).

You can then select the regular Paint Brush Tool in the Affinity Photo Tools Palette. We will use this to paint black onto the mask where we want to hide the colour replacement.

With the brush tool selected, change the foreground paint colour to black in the Swatches Studio Panel.

Now click on the new Mask in the Layers Studio Panel to ensure it’s selected. You can then paint over areas of the image where you want to hide the green. When doing this it’s probably a good idea to have the Paint Brush set to 100% Opacity and Hardness in the Affinity Photo toolbar. This will make it easier to paint the mask accurately.

If you do mistakenly reveal any red, you could undo the brush stroke to make it again using the Undo menu. Alternatively, switch to painting with white on the mask by pressing the letter X on your keyboard. You can then paint over the red areas to reveal the green layer again.

edge of the boat following the colour replacement clean up

The trick to making the clean-up work is to paint slowly and use the brush at 100% opacity, with 100% flow and 100% hardness. When you zoom in close to a high magnification like 100% you can mask out the unwanted colour with a high degree of accuracy.

If you want to know more about working with Layer Masks in Affinity Photo, see my book Affinity Photo How To.

Colour Replacement Brush Limitation

When used to replace bright colours as in this image, the Affinity Photo Colour Replacement Brush seems to work like magic. This is especially true when you understand how to refine the results using the different brush controls.

There is however a limitation you might encounter. If the colour you want to replace is black, grey, or white the Colour Replacement Brush won’t work. It only works on pixels where they have an actual colour to replace. Also, when a colour is weak because the RGB colour channels have similar values, the Colour Replacement Brush has a reduced response. This means you can’t replace a subtle colour that’s almost grey with a strong colour.

Using Affinity Photo Colour Replacement Brush Summary

We’ve now looked at the main features of the Colour Replacement Brush in Affinity Photo. The key points to remember when using this tool are:

  • Work on a copy image layer as the Affinity Photo Colour Replacement Brush is a destructive edit.
  • Use the preview feature of the brush to check the colour before you start painting.
  • Use the Continuous Sample and Tolerance settings for greater precision.
  • If you make any mistakes use the Undo option or use a mask later to fix it.
  • Magnify your image whilst working on detail. Changing the magnification makes checking and fixing areas easier.
  • Using a hard-edged brush at 100% Opacity can make replacing colours easier and produce more convincing results.

The Colour Replacement Brush isn’t the only option for replacing the colour of an object in Affinity Photo. It’s also possible to make similar colour changes using the HSL Adjustment layer.

You might also find the following video helpful in understanding the Colour Replacement Brush Tool.

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