recommended dye for getting PBT caps as close to solid black as possible?

[jacobolus]

I have some old Apple Extended Keyboard II keycaps which I want to use in kind of funky experimental layouts, where the existing legends won’t correspond at all to the logical key functions, so I want to make them blank black if I can.

Can anyone recommend a dye to use to get PBT as uniform black as possible? Or a few possible options to test would be fine: I’m happy to do some experimenting, though I probably won’t get around to actually doing this for a few weeks at earliest.

[strict]

I think people have been using iDye Poly lately with good results

[fohat.digs]

I always go back to this:

https://geekhack.org/index.php?topic=35444.msg658453#msg658453

RIT dye worked perfectly for me with black, and I was able to re-use a bottle of dye-water a couple of times (just took a little longer). But I think that I had an old pack and they changed the formula a couple of years ago.