I used Krylon Fusion Navy Blue on the back of a Eclipse 12 tank (acrylic) and it worked great. Looks similar to the backing 'cobalt blue' used in Seaclear aquariums. It adhered to the acrylic nicely and looks great.
I picked up the Eclipse 12 from Petsmart. Someone had gutted the filtration unit from it, but I still got the acrylic tank, hood, lights for $30. Picked up a cheap Whisper internal filter and am going to use it for QT