Printed key caps (using keycaps.pk2):

If a 3D printer does not support multiple materials, the final model can be painted by permanent markers. I found that the Sharpie felt-tip pens are durable and well-adhesive to PLA.

The model texture is formed by parallel lines (at side surfaces) or cross-hatched pattern on top and bottom ones, and the ink flows in those micro cracks, thus spoiling the painted regions. So I performed a trick:

1. Made a model as if it is two-material.
2. Setup a slicer for two headed printer having zero offsets.
3. Removed all Tn commands in resulting G-Code text file.

Resulting model texture is having etched contours of inter-color borders, and the ink of different color don't intermix.

Keys "TGBYHN" are raised by 2 millimeters:

Thumb caps are too long and unsteady, so I'm going to redesign them.

Here is the assembled keyboard from top (this time having full wiring):

Now I've started coding the firmware. This code looks useable for mouse sensor Dwergmuis