Can I paint a carbon fiber tank!?

The specifics of your question are in the CGA Pamphlet C-6.2 of which I have not been able to find a viewable copy of online. When I inspect steel and aluminum cylinders (Propane) I look for defects, paint doesn't matter. There are currently no composite propane cylinders approved for use, so I don't get to inspect those. From what I have read in the CFR 49 Part 205.180(c) there is no restriction on painting a carbon fiber cylinder, only a coating that would impede the visual inspection. Propane cylinders have this same requirement (no rubber, tar or similar substances). Paint won't conceal a defect in a cylinder unless it is very thick. 
 
You could put a bunch of Airgun Nation stickers on it. :)
I printed a reference sheet that has the "sweet spot" fill pressures for all my rifles, how many shots to expect, what pressure to refill at, and average fps that the rifles are shooting at. Then I just taped it on with packing tape. I find it very handy. Having multiple rifles, I don't have to try to remember what the right fill pressure is anymore, I just look. on the bottle. I might also make a BAR vs PSI chart and put that on there. 
Whatever you do, just don't cover up the important numbers from the factory and hydro date labels. 
You could also get a scuba tank mesh net that might accent the color nicely and protect your tank at the same time! 
Tom