I would like to make some custom size keycaps, and would like the legend to be embedded in the cap (not painted on).

FDM printers can use two extruders, but I don't think they have the resolution. The Prusa i3 MK3S with multi-material might be able to do it with a 0.015mm nozzle.

I am told that SLA or SLS is the way to go, but that gets me one color. Would it be possible to print a keycap with the a negative-space legend (not sure how to describe it). A hole left behind in the shape of the text.
The idea being to manually pour a different resin in later? Would it even cure?

Is there a better process?

I'd like quality that approaches injection molding. And a legend that doesn't wear off easily.