Black backgrounds vs Blue vs none? It doesn't effect the rest of the light hitting the coral. The light would most likely be of such poor quality and intensity, it wouldn't be worth it. The light that would be reflected in the first place, or not, would make minimal, (not to mention impossible to quantify), impact on overall coral health to quantify.
Black, Blue, Pink, or Yellow backgrounds are for personal preference, not performance.
BTW, the drawings look good online, quit stalling and do a real thread!!!