Color Modes (Layer)

You can specify a color mode for the pixels of your layer. This will restrict the colors used for displaying as well as blending. Most modes are non-destructive (with the exception of Indexed mode). You will notice that certain visual elements, such as the palette and color picker, will change the colors they display in order to match the mode.

These color modes can be used for artistic or proofing purposes, but they will additionally allow you to save flattened images with those restricted colors. Loading such a restricted image will automatically specify the color mode.

Global vs Per Layer

Color modes can be independently applied to individual layers (resulting in a true color image), or they can be applied "globally" to the image as a whoe. Global color mode allows you to more accurately restrict colors to support specific flattened formats.

When editing animated GIFs, the format itself can support per-layer palettes or a single global palette.

Predefined color modes

True Color

True Color is the default mode which does not apply any restrictions to the colors in the layer.

High Color

High Color is a 16-bit "565" format (5 bits red, 6 bits green, 5 bits blue).

Web Safe

This is a historical list of 216 colors that are designed to be reasonably likely to display the same across devices with limited palettes.

Grayscale

The Grayscale mode restricts your image to 256 shades of gray.

One use of this is in the Decompose feature which splits a layer into three layers, one for each color channel. The Grayscale mode here ensures an accurate representation of a single layer before it is blended.

Another use is when editing a layer mask, which is inherently monochromatic.

Bitmap

The Bitmap mode reduces your image to a single bit of color (black or white).

Palettized modes

These modes allow you to work with a custom palette. The palette can be generated from your image or you can apply a predefined palette instead. You will be prompted to create a palette when switching modes.

Indexed

The Indexed mode changes how pixel data is interpreted, and as such is inherently destructive when applied. The image data can contain up to 256 distinct colors, and you can modify the palette independently of the image data for artistic effects.

When in indexed mode, some drawing tools are disabled or limited in their functionality. Color-based filters can apply to the palette instead of the image data, which allows you to quickly recolor GIFs for example.

When in global indexed mode, there are additional restrictions on how layers can be blended. Blending modes are not supported, and only 1-bit transparency can be used between the layers (either as an alpha bit or transparent color). Layer masks can only contain 1 bit as well.

Palette

The Palette mode restricts your image to a specific color palette. Unlike Indexed mode, the restriction is applied after any blending is performed, so drawing tools can be used normally. However, you cannot modify the palette independently to recolor the image.

Reduce Color Depth command

You can destructively reduce the number of colors in your image without switching modes by using the Reduce Color Depth command in the Color menu. You will be presented with the same options for generating or choosing a palette. However, this operation only applies once and does not switch the color mode.