To go along with the plain white idea, I rigged roll down opaque white (blackout) shades that I got from IKEA. Super easy to roll up out of the way and down when I am done. I only grow seedlings indoors for the 3 months before plant out so I don't know if my setup is good enough for an all year indoor greenhouse which I think is what you're wanting to do.
BTW all those Egyptian onion bulbs sprouted just fine and are trucking along...
In the pic below you can see the rolldown shade... the back is just the white wall... complete with little fans to help everyone get strong!
