we use black board paint or spray cans,
i find black is better because it gives you depth, if you look at a tank with black on it you think the tank is bigger, blue brings the back of the tank closer to you, one side of my shop has the back of the tanks black and the other side of the shop has blue backed tanks and everyone thinks the black backed tanks are bigger.
thats why black is best and it doesnt show algae as bad