How can I achieve a rainbow colored chrome finish over aluminum?

My name is Jason Jordan. I have a small automobile performance parts brand. I'm trying to get more info on how to achieve a chrome-like rainbow colored finish to be applied to aluminum parts.
Here are pictures:

Hi, Jason. This finish, which some people call Aurora [I don't know whether it's a trademark], is still a closely held secret. But I believe that the coloration is a diffraction effect from varying thicknesses of titanium anodizing. This, of course, leaves the question of how is the titanium put onto the aluminum and how is it anodized to varying thicknesses.

I would tend towards believing that the titanium is applied by a PVD (physical vapor deposition) vacuum process onto highly polished aluminum. Although different colors can be obtained by using varying voltages, I can't see a practical way of applying varying voltages, so I think a single high voltage may be used and varying immersion times achieved by multiple dipping. Some parts that I've seen pictures of seem like they may have been selectively buffed/polished before anodizing such that the titanium is buffed to extreme thinness in some areas, such that perhaps the thickness of the titanium is the limiting factor governing the thickness of the titanium anodizing.

It is an impressive finish that still commands a high premium.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey