To recolor RGB-defined regions independently in Affinity Photo, save each channel as a spare channel, then use its selection to mask a separate fill or adjustment layer. This Mac workflow keeps the source artwork and replacement colors editable.

The steps below use Affinity Photo 2’s desktop menus and an original abstract composition: a red ellipse, green rounded rectangle, and blue triangle on black. The goal is three independently adjustable replacement colors, each confined to its original region. Affinity documents channel-based selections and masked adjustments as supported operations. Spare channels

When do RGB channels give you separate regions?

An RGB channel contains component information across the image; it does not automatically identify one object. Affinity creates channel selections according to each pixel’s contribution from that channel, including partial selections. This makes pure, separated RGB shapes a useful starting point. Using channels, Pixel selections from channels

The following table is an illustrative prediction for opaque, flat colors in an 8-bit RGB document. It describes interior pixels; softened edges can contain intermediate values.

Original pixel RGB values Red-channel selection Green-channel selection Blue-channel selection
Pure red 255, 0, 0 Full None None
Pure green 0, 255, 0 None Full None
Pure blue 0, 0, 255 None None Full
Black 0, 0, 0 None None None
White 255, 255, 255 Full Full Full
Yellow 255, 255, 0 Full Full None

This explains two common surprises. A white background belongs to all three channel selections, while yellow belongs to both red and green. If your composition contains those colors, channel masks will overlap. Before building the layers, decide whether you want component-weighted recoloring or three exclusive shape regions.

For this tutorial, use nonoverlapping pure RGB shapes on black. If the shapes already exist as separate editable vector objects and you only need new solid colors, changing their fills directly is the shorter task. The channel workflow is useful when you need reusable masks or are working from a combined image.

Prepare an abstract source without discarding the shapes

Create an RGB document; an illustrative canvas size is 1200 × 800 pixels. Draw a rectangle covering the canvas and give it a black fill. Above it, draw an ellipse, rounded rectangle, and triangle with space between them. Affinity’s shape tools let you drag to create shapes and adjust their properties afterward. Draw and edit geometric shapes

Use these sample fill values: ellipse #FF0000, rounded rectangle #00FF00, and triangle #0000FF. Remove strokes, use full opacity, and omit gradients or effects for this first pass. These are example design choices intended to make the channel separation easy to inspect.

Keep the original shape layers. To make a stable combined source, leave only the intended artwork visible, Control-click a layer in the Layers panel, and choose Merge Visible. Affinity creates a new merged copy above the selected layer. Rename that copy RGB source, position it above the original artwork, and hide the original layers. Merging and flattening

The merged copy provides the pixels for extracting masks; the hidden shapes preserve editable geometry. You do not need to rasterize those originals. Rasterization converts vector content to pixels, after which its vector properties are unavailable on that converted layer. Rasterizing

Save all three source channels before recoloring

Open Window → Channels in the Photo Persona. The panel contains whole-image channels, channels for the selected layer, the current pixel selection, and any saved spare channels. Selecting different layers changes the relevant layer-channel entries. Masking from channels, Channels panel

  1. Select RGB source in the Layers panel.
  2. In Channels, locate the selected layer’s red channel. Its name includes the layer name; distinguish it from the whole-image composite red channel.
  3. Control-click that layer-channel entry and choose Create Spare Channel.
  4. Rename the saved channel Red region.
  5. Repeat for the source layer’s green and blue channels, naming them Green region and Blue region.

Affinity documents creating spare channels from individual layer channels and renaming them for later use. Capture all three from the unchanged source before adding replacement colors so the masks share the same starting image. Pixel selections from channels, Editing channels

Preview each saved channel before proceeding. For this sample, the intended shape should appear white against black, with intermediate tones limited mainly to its edge. If you isolated a channel for inspection, restore the red, green, and blue channels’ visibility before judging the color result. Masking from channels

Treat the spare channels as saved snapshots of the source regions. If you later move or reshape the original artwork, plan to rebuild the corresponding masks rather than expecting the saved selections to follow the objects.

Build three editable colors with separate masks

For flat abstract graphics, a masked fill layer provides direct control over the replacement color. Affinity fill layers contain adjustable solid or gradient colors, and their solid colors can be changed through the Color or Swatches panel. Fill layers

Make the first masked fill

  1. Choose Select → Deselect to clear any previous selection.
  2. Select RGB source, then choose Layer → New Fill Layer.
  3. Set the new fill to an illustrative orange, #FF8A3D, and rename it Red region — orange.
  4. Control-click the saved Red region channel and choose Load to Pixel Selection.
  5. Return to Layers and select the orange fill layer.
  6. Choose Layer → New Mask Layer.
  7. Choose Select → Deselect.

Creating a mask while a pixel selection is active restricts the selected layer to that selection. Check that the mask is attached beneath the orange fill in the layer hierarchy. Affinity normally attaches a newly created mask to the selected layer. Layer masks

Repeat for green and blue

Create two more fill layers above the source. For each, load the appropriate saved channel, select that fill, create its mask, and deselect. Example replacement colors are mint #63D6AC for Green region and violet #9471E8 for Blue region. Keep each fill’s blend mode at Normal and opacity at 100% for this flat-color example.

Your intended layer order, from top to bottom, is:

  • Blue region — violet, with its blue-region mask attached.
  • Green region — mint, with its green-region mask attached.
  • Red region — orange, with its red-region mask attached.
  • RGB source.
  • Hidden original shape layers.

The three solid interiors should now have independent colors. To revise one, select its fill thumbnail and change the color. To revise its coverage, select its mask. Keep those two operations distinct: one changes the replacement color, and the other changes where it appears.

When should you use a Recolor adjustment instead?

Choose a masked Recolor adjustment when you want to tint a region that contains tonal variation. Its Hue, Saturation, and Lightness controls adjust the tint, color intensity, and brightness. A solid fill is more straightforward when the task requires a particular flat replacement color. Recolor adjustment

To use this alternative, hide the corresponding replacement fill first. Load its saved spare channel with Load to Pixel Selection, then select the source and choose Layer → New Adjustment Layer → Recolor. An active selection automatically masks a newly added adjustment. Deselect, then adjust the color controls. Applying adjustments

Repeat for the other channels if all three regions need adjustment-based recoloring. Double-click an adjustment thumbnail to reopen its controls. If the document contains additional visible artwork, make the adjustment a child of the intended source layer to limit its scope; otherwise, adjustments affect layers below them. Using adjustment layers

Diagnose overlap, weak coverage, and edge fringes

Use this sequence before changing colors repeatedly:

  1. A fill covers the canvas: Check that its mask is attached and that you loaded the correct spare channel before creating it.
  2. The preview remains monochrome or oddly colored: Restore RGB channel visibility. The Channels panel’s Reset control returns channel settings to their defaults. Channels panel
  3. A selected region seems incomplete: Inspect the mask rather than relying only on the selection marquee. Affinity displays marquee edges only where selection exceeds 50%; weaker selection can still exist outside them. Pixel selections from channels
  4. Two colors affect the same area: Inspect the original pixel colors. Mixed RGB components can legitimately enter more than one channel selection.

For overlap, Affinity supports loading one saved channel and using another channel’s Subtract From Pixel Selection command before creating the adjustment. This can reduce unwanted coverage, but it also changes the selection: a region shared by both channels may be removed. Preserve the original spare channels and test the subtraction on a new selection. Editing channels

At softened edges, inspect the result at 100% zoom against the intended background. Partial channel values create partial mask coverage, so the original source may remain visible beneath a replacement fill. For a small correction, select the mask and paint black to hide coverage or white to restore it. Layer masks

If the artwork contains extensive gradients or overlapping mixed colors, decide explicitly which output region should own each shared area. RGB components alone do not encode that design decision. For a few original shapes, returning to their editable outlines may be more useful than repeatedly subtracting channels.

Preserve the editable master

Keep fill layers, adjustment layers, and masks separate while revising. A mask can be edited or discarded without erasing the source. However, painting or applying a destructive filter directly to a spare channel changes that saved channel; duplicate it before experimenting. Layer masks, Editing channels

Avoid Merge in an adjustment dialog while you still need its independent controls. Likewise, merging layers removes their separate editability, and Document → Flatten produces a single-layer document. Using adjustment layers, Merging and flattening

Save the master through File → Save As as an .afphoto project, which preserves project information for later editing. Finish by toggling each recolor layer individually: its intended shape should change while the other two remain stable. With the source, saved channels, and masks retained, future palette changes require editing colors rather than rebuilding selections. Save

Sources