Background color choice may depend on your type of tank, and more importantly your fish. Eg. many blue discus tend to darken with a black background or pepper up in the case of pigeon blood colors (something about the appearance of the void may frighten them). Some Tropheus, like Moliro reds, may not show their brightest color with a black background (unless you've got some nice white gravel). However, blue can be quite blaring (this is subjective), especially on a tank without much front to back space and lighting towards the rear instead of at the front (works better on bigger tanks). Some of the lighter colored fish, such as platinum angelfish or small tetras, seem to get drowned out. Now, black works well with cardinal tetras, platinum/silver colored fish (bala sharks, platinum angelfish), electric blue haps. I've found lighter blue works well with discus, black colored fish like mollies and black angelfish. I'd suggest buying some different colored boards and taping them to the back of the tank to get an idea. Alternatively, I've used an pastel green, it looks awesome (very natural looking if you've got a deep tank from front to back).

As for paint, I've used Krylon and Rustoleum, they last. Currently, since all my tanks are nanos now (prior the smallest thing I had was a 50 gallon sump for my smallest tank 250gal- so it pays to planout backgrounds) I buy either colored foam sheets/paper (at Micheal's), or a roll of rubber kitchen drawer liner (comes in black,beige, and white at Lowe's) to clip or tape onto the back of my tanks. When you do paint your tank, especially if it's a large one, having a flashlight or small lamp may be handy, to check for areas where the paint may not be thick enough. Spray on thin coats at a time. Take frequent breaks and wear a mask, this stuff is MUCHO TOXIC!