I am partial to blue, I think it makes the reds and purples pop a little more but that's just my opinion. I would look at what inhabitants you have and do a color comparison. If you have blue fish, them a blue background might not allow them to pop as much. Even with a picture it would be hard to tell since we all know how much things look different to the eye when it comes to our lighting water effects and inhabitants.
Glad to help muddy the water more
