Black Pro Micro from Aliexpress
Found these for sale on Aliexpress. Several sellers have them. They are also usually cheaper than the usual blue Pro Micros.There is now another black Pro Micro that is not the same size as a regular Pro Micro.
Other than having black soldermask, these are unusual as they use the larger ATmega32u4 package. It's the same chip as on the regular Pro Micro (44QFN), but in a larger form factor (44TQFP). They had to move the other components around to fit the larger chip.
The larger chip could make it easier to solder wires directly to the pins to make use of some of the extra io.
The power circuit seems to be identical to the blue Pro Micro's. It does not suffer from the problem the green Pro Micro does, and works fine in split keyboards.
Top view. The chip barely fits on the board. This one has a green power LED and red TX/RX LEDs.
Bottom view. No components. I have not seen any 3.3v ones for sale. Only 5v, 16Mhz ones.
This is how it was packaged. It came with two 12pin headers.
Side by side with the usual blue Pro Micro clone.
Two installed in a foobar.