From Creatures Wikia
"Rainbow spew" is the Creatures term given to the effect of attempting to display a texture or sprite in the wrong color depth. For example, if a program tries to load a 24-bit bitmap as a 16-bit bitmap, it will read the first two bytes, instead of the first three, and attempt to display that color as the first pixel, then read
|What is stored||8||C||C||3||2||A||9||0||3||0||C||1|
|What is displayed||8||C||C||3||2||A||9||0|
See also 555/565.