For this area, each black or white region must contain exactly 2 diamonds of the same colour. No more, no less. For puzzles with multiple coloured diamonds, you can have them occupy the same region. Just as long there is only 2 of those of the same colour.
I also work on the nearby puzzles that has more than one ruleset. In this case, the numbers and diamonds.
If there's only one diamond of a certain colour, you'll need to pair it up with another puzzle element from a different ruleset that is the same colour as the target diamond.