Is anyone else in need of / willing to write such a shader?
(To my knowledge "set color" is the closest effect so far, but it affects the entire sprite. Cloning the sprite numerous times, erasing 1 color each, stacking them, and applying the set color effect seems to be the only option right now, but that's pretty inefficient.)
Also, the Image Manipulator object in CC allowed you to retrieve the RGB value of a point on an image. Like if the color was solid blue on the x,y coordinates (5,10) it would return 0,0,255. It was great for using actual palette images instead of entering the RGB values by hand. Is that possible in C2? I haven't really kept up with the 3rd party plugins so..