This filter only works with RGB images. It is a fantastic tool for adjusting a particular colour in a photographic image or for altering the colour balance and intensity of certain areas in a design in preparation for separating to layers. You can choose to slightly adjust the existing colour using HSL sliders, or replace the existing colour completely using an RGB algorithm
Instructions
- Open the Filter Browser, and add a new filter set using the small + icon located in the middle of the browser. This will create a new ‘untitled’ filter set for you. This will appear in the top section of the Filter Browser. If you already have filter sets created, clicking the + button will duplicate the selected filter set.
- Select Replace Colour from the list of available filters in the lower section of the Filter Browser.
- Double click on the name of the new filter set in the top section of the browser, and name it appropriately.
- Using the Pipette Tool, click on the colour you wish to replace, then drag this colour into the filter.
Adjusting the existing colour slightly
- Change the Mode to HSL.
- Tick Preview at the bottom of the Filter Browser.
- Adjust the H, S and L sliders to change the selected colour to a different hue, saturation or lightness level.
Scale
The Scale setting is most effective when used in conjunction with the Mask option. 
Mask can be used to separate out areas of the design. These areas can either be created as new layers simply by pressing the New Layer button at the bottom of the Filter Browser Window, or they can be converted to selections for you to edit further.
The lower the scale, the more information you will be adding to the layer.
As you increase the scale, you remove information from the layer.
Tip: If you want to see the exact area you are adjusting, temporarily change the mode to Mask. This displays a greyscale view of the information being altered. You can create a layer from this mask by pressing New Layer at the bottom of the Filter Browser.
Changing the existing colour to a specified colour
- Select the colour you want to change from the image with the Pipette Tool and drag it from the foreground colour in the Tools Palette into the colour block beside the Replace Colour popup menu.
- Change the Mode to RGB. You will notice a second colour block appear in the filter settings.
- Change this colour by either ⌥ (option key) clicking on it to open the Colour Picker, double clicking on it to select a colour from a colour file, or by dragging a colour to it from the Swatches Palette.
- The colour changes are applied in real time to the image
Applying the filter
There are several ways to apply a filter:
- Click Apply - this will apply the filter to the active layer(s), and within a selection if there is one present in your file
- Click Make Layer - this will make a new layer in your file containing the filtered effect, leaving the original layer untouched
- Apply the filter using the Brush Tool - when you have finished building your filter set, simply close the Filter Browser. Then, open the Brushes Library, and select the filter you have just made from the drop down menu shown in the snapshot below. You can now paint with your filter.
Note: The default setting for the Brush Tool is ‘Brush”, located at the top of this drop down menu. To prevent you from becoming confused between the default setting and a filter setting, do not name any filters ‘Brush’. When you have finished painting with your filter, set the drop down menu back to the Brush setting, otherwise the Brush Tool may not behave as you would expect later on.