"Colorizer" is a simple paint program for Atari 8-bit computers
which allows you to change or add color in APAC images.
"APAC" ("Any Point, Any Color") images are made up of two separate images
in two different "GTIA" graphics chip modes. (GTIA was included in
later Atari 800 models, and all 8-bit computer systems after that.)
A 16 greyscale ("GRAPHICS 9") mode image, and a 16 color
("GRAPHICS 11") mode image are combined via interlacing or flickering,
to give a total of 256 different perceived color possibilities at
a resolution of 80x96 pixels.