AfaIk you can get Ti bolts in Ti finish as well as blue or gold. The colours are to do with the surface treatment. Gold is nitride (like some of the Pace stanchions or drill bits) but I'm not sure what the blue is. :?
The difinitive. . .
al can be anodised, and the surface is receptive to a dye before it is sealed. There are therefore many colour options available. Ti can be ano only in the sense that the surface takes on a hue due to the applied anodising voltage, no dye involved (think of it as a 'colours in an oily puddle' type diffraction). Thefore only spectral colours are really available.
Some military stuff uses coloured ti fittings (thinking of eurofighter parts and hoses), but because the process is pretty variable, its didn't work too consistently well, or well enough to conform to the appropriate def. standard for "identifying" colours. .