Colorize

Colorize[values]: returns an image where each number in the rectangular matrix values is a pixel and each occurrence of the same number is displayed in the same unique color, which is different from the colors of all non-identical numbers.
Colorize[image]: gives a colorized version of image.

- Colorize[{{1.3, 2.1, 1.5}, {1.3, 1.3, 2.1}, {1.3, 2.1, 1.5}}]
- Colorize[{{1, 2}, {2, 2}, {2, 3}}, ColorFunction -> (Blend[{White, Blue}, #]&)]