Windex every time you touch it...or don't touch it, it's just the nature of Ti anodizing.
It happens because Ti doesn't actually change color when anodized, a clear oxide layer is built which refracts a different wavelength depending on the thickness resulting in it appearing to be colored. The oil in your fingerprints dulls the effect. That's also why it's almost impossible to get decent pics without full spectrum lighting.
~Chip