Cool set up. Yea black absorbs light. On my little cube I used a black corrugated plastic so I Can take it off later. Maybe.
Any luck on the single t5? I got say I'm kinda in love with the current orbit. Not as much par as a t5 but I don't think you need it. The ramp up and the coral pop is really cool in the morning and at night. A Sweet Royal blue. The older version sells for 75 to 100 bucks. Here or eBay.