Although I like the feel of the stock PBT keycaps on the Leopold FC660M, the monochrome color scheme with yellow legends on dark brown keycaps was not sufficiently legible for me. My initial modification used dye sub PBT white and gray Cyrillic sets, but having both English and Cyrillic legends was a bit too busy. So, I harvested the white-on-black keycaps from a Cherry G81-7000-HPBUS-2 keyboard and used these with black-on-white modifiers from the Cyrillic set (the modifiers have English legends only).
The result is highly legible, and the use of white-on-black for the arrow keys and insert/delete keys makes these keys blend nicely with the rest of the board.
Note that I still need to get an additional black-on-white left shift. The FC660M accommodates the arrow cluster by reducing the right shift to the same size as the left shift. I am temporarily using the zero key from the numerical keypad as a right-shift key.
Being able to customize the keycaps in various ways makes the Leopold FC660M all the more attractive as a sub-tenkeyless or 60%+ board. It would be even better if Leopold would use standard stem spacing on its spacebars.
