] Again, makes me wonder if it is a French colour-word from French journals as French Fashions were supposedly the height of fashion and the richest, chicest and most pretentious English women aspired to copy them

JA also mentions the color in one of her letters to Cassandra, and she certainly seems to be having some fun with it:

I took the liberty a few days ago of asking your black velvet bonnet to lend me its cawl, which it very readily did, and by which I have been enabled to give a considerable improvement of dignity to cap, which was before too nidgetty to please me. I shall wear it on Thursday, but I hope you will not be offended with me for following your advice as to its ornaments only in part. I still venture to retain the narrow silver round it, put twice round without any bow, and instead of the black military feather shall put in the coquelicot one as being smarter, and besides coquelicot is to be all the fashion this winter. After the ball I shall probably make it entirely black.

But now I wonder... anyone know what nidgetty means exactly?