Once more, thanks for all your support.
As reversing some colors looks too complicated, I think I would create a bold or semibold 10x16, or try to use a 12x16 font for the ST7335 (some reason for not being an option on the current config644.h?).
BTW: I looked into the 12x16_hf and spotted 3 errors (flipped first diode, wrong Ä, and the Ü=ü) (iirc, somebody already reported the diode error). If that font is viable, I'll look how to fix those characters.