Yes absolutely agree. Colourful jewels such as these need plain clothes such as black to show them off to their best. It may well have been the photographer who asked for the black - and what an inspirational choice.
Here is a web page from a magazine that shows several of his pictures including the one of the Duchess.
--Previous Message-- : --Previous Message-- : I saw this parure once, and it is amazing. : I : think the Duchess was wearing the tiara and : the necklace, given her hair and the drops. : I think this was just intended to be a : clever portrait. Thanks for the picture! : : : I agree. No photoshopping here, not even for : the stomacher. A clever portrait - and a : priceless facial expression! : And that fabulous Lucien Freud portrait of : hers! : :