I bought my GT Xizang - a titanium-framed hardtail mountain bike - new in 1995, and love her more every day. I wouldn't dare paint over her polished bare metal skin. In fact, I've intentionally let the original factory stickers slowly scratch and scuff off in an attempt to make her less appealing to bike theives.
I have purchased TWO new complete sets of original factory stickers, for when I'm eventually ready to take her back to brand new appearance.
I'm amazed that the bike manufacturers don't make use of 3-M reflective material for their OEM stickers. The head badge and the make and model stickers they place on the top tube and down tubes are perfect places for reflective material, in the interest of rider safety.
But I think polished, bare naked shiny titanium stands alone in beauty. You can't fix perfection.