UPDATE: Hi John, I’ve been thinking about colours and I wonder if the answer is to close crop them into squares and add coloured frames with no mount? I’ve mocked some up and they look really bright and contemporary without losing any of the intricate nature of the drawings. And as you suggested, to curate them in closely hung sets of four could look great. I think we could use Neilsen aliminium frames (500 x 500), or find a company that do them in primary colours?
Solid primary coloured frames
Primary coloured group
Gold frames (or copper) from Neilsen