I went down the black route for my tank, went to a local sign makers and got a sheet of vinyl cut to the perfect size for a couple of quid. That way you can take it off and change the colour at a later date if you want! Just mix a tiny tiny drop of washing up liquid in a spray bottle (garden spray thing?) the give the outside of the tank a couple of squirts before putting the vinyl on. If you use filler blades you can make sure there aren't any bubbles either.