Do black and white scanned darks work on EMI's

Stick to color works always, BW is not always accepted and you risk that EMI's refuse it. Back in time where a normal color scanner or smartphone wasn't that used, black and white docs were ok, but not today.

High Resolution color scan are required by most of the EMI's and payment processors, B & W is only accepted on occasions.

don't use such darks, you ask for trouble and redo.

I have always only used High Resolution color documents when used, they pass allways.