In general the FR4 plates you see sold are basically "componentless, padless PCBs". They are manufactured in the same way as PCBs, at the same factories, but of course with the specific switch cutouts to make them work as plates. Most commonly 14mm squares with 0.5mm radii and 19.05mm spacing for MX switches.
The colored paint you see is not paint at all; it's called soldermask, and acts as a solder repellant in PCBs so as to avoid shorting two pads together. The aesthetic function of them is secondary, but together with the silkscreen they can be used to make some nice graphics and stuff like that.
