It looks like all the color coated titanium models suffer from color shift due to fingerprints/sweat. The blue is the worst affected, as you use it, the blue color where you frequently touch the phone, such as the buttons, it starts changing from dark blue to light blue and looks ugly. Can it can be fixed by deep cleaning or polishing the phone and then it goes back to the original color.
Only the natural titanium is not affected by this
Interesting. I was having quite a tough time of deciding what colour to get so natural might just be the safest bet.