I've tried Green and Blue - because they came with my light, I think I was supposed to get red and blue according to teh package.
The green is ugly, it makes the pool look like a big algae bloom has set in, might be good around Halloween, even then, I'd prefer blood red I think! Then again, I can't stand Green on anything except what nature makes (trees/grass etc.)
The blue looks really cool, it takes away the brightness of the bulb nicely and gives your water a really clean look - it seems to make it look like you have a darker liner - I really like the look of blue, but I'm sure, like anything it's personal preference.