Okay, I've gotten a little futher on this -- but have run into a possible bug... I am changing the color filter on my nebula sprite over time. This expression:
Sprite.NebulaBlue Set Color filter to: rgb((getred(NebulaBlue.filter)-10*timedelta),getgreen((NebulaBlue.Filter)-10*timedelta),255)
Works great. I can get it to drop both the red and green values for the sprite's color filter down to 0.... But trying to do the opposite (adding TimeDelta instead of subtracting):
Sprite Set Color filter to: rgb((getred(NebulaBlue.filter)+10*timedelta),getgreen((NebulaBlue.Filter)+10*timedelta),255)
Doesn't seem to do anything, the red and green values stay the same. Anyone have any idea what I am missing?