The color mode of an sprite or image specifies the internal structure of each pixel. You can see the Color Mode section in the Aseprite docs for an introduction about each color mode.
You can use this color mode to create RGBA sprites and images.
Each pixel is a 32-bit unsigned integer where each component (Red, Green, Blue, and Alpha) uses 8-bit (values from 0 to 255).
You can use this color mode to create gray
sprites and images.
Known as ColorMode.GRAYSCALE in previous versions.
Each pixel is a 16-bit unsigned integer where each component (Gray and Alpha) uses 8-bit (values from 0 to 255).
You can use this color mode to create indexed sprites and images.
Each pixel is an 8-bit unsigned integer (a value from 0 to 255) which indicates the specific palette entry which the pixel refers.