The inside of mine is black it's nice and clean.... Makes it a little dark where I had to add a light but no big deal it's better than boring white haha..
We finished our reef stand with stain and varnish on the inside to match the out. I think it looks alot better than white, especially after the white gets dirty and ugly.
There was one on RC that the guy painted the inside of his stand/canopy a bright sky blue. I doubt it did anything for lighting, but was certainly interesting.