Compare the visual similarity of two colors in code with color_compare_simple! Does your player need to mix potions to get the right color? Maybe your game features an animal who needs to hide in a place where they're well camouflaged. Now you can easily test the visual similarity between two colors with this GML script.
color_compare_simple( color1, color2 );
Returns a value between 0 and 1, where 0 means the colors are complete opposites and 1 means the colors are exactly the same.
Difference between this and Chequered Ink's CIE scripts
This script is simplified, easy to modify and doesn't have the potential "divide by zero" problem that the other scripts were prone to (due to GameMaker rounding very low values).