So like a Fillcan that paints all the bricks a random color?
Tell me if Im wrong
Yes, you are, sadly. It's just that every brick gets colored randomly.
Thanks. I'll pretend that meant something.
Fine, I'll explain this, then someone will point out irrelevant flaws.
FX is effects. Special animations of the layer used for coloring. Things like rainbow and blink are special FX. They change the brick on a constant basis, working with the engine. A spraycan mode that simply sets every brick it paints a different, random, regular color is not FX. It's just setting random colors. If you've ever examined a large consistent area of Rainbowed bricks, you'd notice it's special layers moving over the bricks that makes it do that.
Again, I still support the general idea, but it shouldn't be under FX. If you need more explanation, I'll bash your head in with a rabbit.