I've actually managed to get all the way to the turqoise end of the Ti spectrum using a MAPP torch on 5mm thick Ti. I think the trick to getting a clean, even coloring is in the surface prep, and *patience*. I asked Chad Nichols a while back, and he recommended cleaning the piece with acetone, then a damp wipe, then wipe dry. After the initial acetone wipe, I handle the work piece with either gloves, or a cloth, so no skin oil contaminates it.
If you have a torch that goes hot enough, you just need to heat it in stages, rather than all at once. I heat until I see the color change, then cool it rapidly with an air fan or blow gently on it. If your desired color is at the further end of the spectrum, I heat it several times, stopping at various colors along the way. The one time I actually tried to heat it up all in one go, parts of the oxide layer got too hot, and flaked off.
I tend also not to water cool the piece until I'm totally satisfied with the color, as even remnants of water drops on the surface can lead to contaminant spots when you heat
