Bernadette, these rings are beautiful!
I would not mind about the colour of the engagement ring stone - I also think black is very unique, and as far as I've heard coloured diamonds are supposed to be more expensive than regular white ones. So that may be a plus, and not everyone has them.
As long as the ring in its shape and the diamond's cut are pretty, that would be fine with me.
OT: I went by a jeweller's yesterday and saw a ring with brown diamonds - one would think it looks weird because brown isn't a special colour at all, but it was combined with pink diamonds and looked sooo pretty.