Some people paint a piece of acrylic (away from the tank) and once it is cured
and dry, put it on the back of the tank for a nice visual effect. I've seen
some amazing ideas on RC in this area, where it gave a look of infinity with
various blue hues.

Marc

everything marc said and if you choose styrene instead of acrylic its cheaper, lighter,
easier to cut .....

and on top of that its opaque and white so you wont have to worry about getting enough
paint so you dont see thru it. and the lighter colors are easier to work with.

--
Richard Reynolds