I had a descent 2' x 2' dispersion grid made of 2" x 2" wood of 5 differing heights in a random pattern and placed in the center of the wall behind my Soundlab U-2s. I built this years ago and stained it dark brown. So, in the new digs, it would look better in black. Stain with ebony or just paint with the black automotive paint I already have? Saved $7 by not buying the stain. WOW, it wrecked the sound. Apparently, the automotive paint is a really hard surface and the high frequencies went ballistic. So, I recommend you consider the impact of hard finish paints on the speakers - which may have a real effect on the sound.
Vincent Raptor