IMO, gloss black is the way to go. (make sure it's water-based paint) the alkyds in oil-based paint could leach in through the silicone and/or glass. First of all, it hides most in tank equipment like powerheads, overflow boxes, intake and outlet tubes, etc. Plus, it also sets off all of the tank's inhabitants because it contrasts W/almost everything. Originally, I painted my 125 reef a blue sea color, and though it looked very "aqua," a lot of the tank's fish blended in W/the background like my blue tang, damsel, and bi-color angel. Again this is just my opinion.