Maybe no useful ones, but I'll say them anyway.

First of all, some people have a distinct and detailed awareness of colour that "normal" people do not. For most people, "very pale peach" and "pale peach" would be visualised differently, and that would be good enough for most purposes. However, a paint colour chart has-what, ten? - different pale peaches and they have to be separately identified.People who make a living working with colour (decorators, make-up artists, painters) have to understand a great deal more about pigments than simply the resultant wall colour, and they use far more words to identify colours. They may well not use the word "red" at all, but refer to Alizarine, Rose Madder, Vermillion, Scarlet, Turkey red, Indian red, or a dozen other reds that are named more for what they are made of than anything else. I think the joke, if there is one..is in the Edgeworth quote that I linked- that here was an artist who was using terminology well beyond that of the average person, to comical effect.

Some particular colour words come into fashion from time to time, for no particular apparent reason, except that they are associated with a particular fashionable shade. I can remember the eighties, when "taupe" became a buzzword. "Taupe" is french for "mole" and I suppose it was used becausethe word sounded more up-market than "mole " or "mouse" would. I'm not sure anyone would buy a dress which was mouse-coloured! Perhaps something similar happened to "coquelicot" in JA's time? Perhaps it was a new colour that was mass-marketed in London, and Isabella (who does seem to have London connections in a very vague way) picked up on it.

Thething about fashion journals was that papaer was an expensive commodity, and I think the authors would have tried to cram as much info into a small space as they could.They may well have used elaborate colour names between themselves, but would they expect their readership to understand them all? With all the other gobbledy-gook about Lady this, and Viscountess that,which was obviously felt necessary they are not leaving themselves much room for elaborate descriptions of subtle colours, are they?

Probably not much help, I know.....