+1 for painting them white, you will not regret it.
Not sure if it was the quality of the OSB or the paint I used but I got some bleed through, probably from some resinous wood chips, or tanin, when I painted mine.
I plasterboarded (drywall to you) mine - with the more fire resistant boards. The ply was a structural element and bit rough to be left as it was and should there ever be a fire, more chance of having something left. So plastered it and then painted it all white.
Very glad as it feels a lot more open and lighter in there.
p.s. If you are going to paint it - do it with an Airless Sprayer. Damn quick!
Thanks gang! Lots of votes for painting them white. I'm pretty sure I'll go that way to maximize the lighting. I'll probably need to use a coat or two of primer to block out the black printing they put on the smooth side of the panels.