SK6812 Mini-E (they're the big legs, but I don't know the component name difference).
They can be per key (not supported on ZMK currently) or just treated as up facing underglow. BUT! The biggest concern I've had is the realization thaht all RGB boards on the market that use SK6812 in bulk don't seem to consider the total peak power consumption.
One color can peak at 12ma at 5v. They're often ran at 3.3 or 3.7v. 3 colors per led for 36ma per led. So on sofie type boards where there's ~30 keys per half you're pulling 1.08ma if you ran the leds at max white. This would be HIGHER if they're run on 3.3v or 3.7v due to the relationship between wattage and voltage. Yet! They've worked fine. I've had good success.
Going forward I'm swapping to SK6805 surface mounted leds. I've got the pick and place running, and the goal is to have per key rgb with underglow. That would almost 1/3rd the amperage requirements. Also gives me a little more board space I'm hoping.
Ideally, I'll have non-rgb options, up facing perkey rgb, underglow, and up and underglow rgb options (probably 2 independent rgb channels aka underglow has its own data pin). All in either Choc v1, MX, and whatever else I decide to support.
I've got a working "screw" mount solution that works! The problem is with the pcbs fitting super well (model dependent) (I've based on the standard dactyl) why bother using lots of screws when a little hot glue does the job. My first versions were wrongly sized and I ended up being extra cautious with lots of extra glue to ensure there's never a issue with pcbs coming free, but at this point I'll either cut the number of screw points down, or honestly supply it but not use it myself.
The nice thing with getting access to production equipement (my designs are all about saving my time in production) you get to save that time too.
Sorry for the silly long response!
Not 100% sure on if you can easily get this consistent. I know that there are ways of dying resin post print though.
I wonder if you can just get evenly tinted semi-clear automotive for it.