There is this:
Thers is de canvas plugin that has this rgbaAt expression.
Personaly i think that you take this 'problem' as to strict. 'colour' can be presented as an instance variable (or family variable). Either as a string or as a number. Use the variable to pick.
If you choose to present the colors with a number, you can (to make it yourself easy) create a event sheet without an assigned layout, and include that in your main sheet. Create global variables there like:
Global variable 'cPurple' ... value 1
Global variable 'cBlue' ... value 2
Now if you gonna compare, it is easier to wrap your mind around it.
if instance variable = cBlue ... then
You can also set the animation speed to zero. (if you dont have animations). Now you make frames that match with the numbers. Frame 1 = Purple. Frame 2 is Blue.
Now you only deal with instances of the same Sprite. And do things like:
Mouse > object clicked > sprite
Sprite > compare frame > =? > Cblue