Jose,
I think the main thing is the stand & canopy color. It you have a dark stain or paint on the stand and canopy it really shows off the tank. IMO the blue background stands out way more w/ the dark stain. So you already have a great color on the stand. ;)

With the size of your tank and your dark colored stand, I dont think sponge painting would take away from your tank.

Its time to go stain now. :-D I have finished the canopy, but am still working on the stand. I will post some pics for you after I finish. It looks like a new tank.