Help making Titanium Purple

Hi, I'm trying to make a titanium lugnut the color purple for a car, for the sole purpose of making it more aesthetically pleasing. I own a performance shop that specializes in wheels and suspension. I am having titanium lugnuts made, and I would like to make just the ends of them purple and blue. I have read you need a current, and an electrolyte bath. My questions are more specific than I have been reading on here. I would like to know the best readily available bath solution, and what voltage I should run through it.

I would like the finish to fade to the end of the lugnut, so how would I do that. Would I have to vary the voltage as I dip them further into the bath? Also, what exact voltage do I need to make the finish Purple?

Here is a picture of what I am trying to accomplish:

According to Oppi Untrachts book on Jewelry Concepts and Technology ⇨
you can use next dc voltage:
20 V-purple
25 V-dark purple
Hope it helps and good luck!As electrolyte you can use even coke or coca cola(or 5% phosphoric acid) !

memory recall-
temp less than 20 c
cathode lead
sulfuric acid around 10%
volts 20 and up colour purple goes to yellow