Has been a long time since I had those discussions. Among my circle, etching involved a nasty chemical like Hydrofluoric acid and only a few makers had used them before going onto safer methods. I'd bought a dry powder that was a ready to mix but after reading the MSDS I sent it in for hazmat recycling. I wasn't going to risk the fumes nor contact in my garage/shop.
https://mrtitanium.info/2011/08/09/q...etch-titanium/
https://www.finishing.com/134/32.shtml
Our approach was to mask/stencil and use a small air eraser with fine mesh media like AO,SC. Then go in with the anodizing solution and paint it in. Old timers like Judy Beaver, Patricia Walker, Jim Sornberger have used similar in their anodized Ti pieces. If you have an anodizer you can have a spectrum of colors. Using the usual marking units yield one color, often in the blue range.
Laser marking is the other.
May contact Marking Methods as see if they have any advice:
626-282-8823
sales@markingmethods.com
If there is a new means, I'd like to explore that too.