The reason the ti wont etch black is because there is no carbon in it,try adding some carbon (rust) to your electrolyte and see if that works. I have tried this and it makes a black mark but I haven't experimented with it enough to get it perfected. Earnie Grospitch led me in this direction,he may have perfected it by now,but I don't know for sure.
We came up with blue marks. Very low power and very quick passes with the Ti designed solution.
I sent a note off to the owner of IMG electro etch and he is going to see if he can come up with something that will give us a darker mark. I will keep you posted.
Ernie's stencil worked okay on 6Al4V but would not work on some 6242 I think that's what it is. A stencil that is cut a little bigger did not give good results at all. Frank