] Hunt though I might, I can't see where I got these references from. These days we seem to stick with fairly simple colour names, like dark red or pale blue.

I do agree with you in general, but 'poetic' colour names are still alive and well in the twenty-first century. Just look at these examples from the Dulux Paint Colour Chart. They all represent various shades of blue:

Azur Oasis, Blue Allure, Blue Lagoon, Blueberry Crush, Dreamboat, Heathland Rock, Instant Indigo, Moonshadow, Nightshade, Silken Sky, Soft Hyacinth...etc etc etc

But, to get us back to Life and Times, here are the only colours (apart from gold and silver) mentioned in the descriptions of the ladies' gowns from my Lady's Pocket Magazine for 1796.

At the celebration of the Queen's Birth-Day, kept as usual this day, the principal Court dresses were:

The Dutchess of York - A green satin train, crape petticoat, richly trimmed.

Princess Sophia - A light blue train, crape petticoat, with knots of flowers, &c.

Marchioness Townsend - A crimson satin, very elegantly trimmed with point lace and deep silver fringe.

Lady Cathcart - A blue satin body and train; white crape petticoat, richly embroidered with gold spangles and twisted stripes of sable fur and gold laurel; the border a beautiful painting on white stain, ornamented with gold points and gold fringes.

Lady Ann Fitzroy - Crape petticoat, richly embroidered with wheat sheafs in gold, and ornamented at bottom with a rich border of marone velvet, gold fringe and tassels; body and train to correspond.

Hon. Miss Eardley - Crape petticoat, a striped applique of white satin and silver, the drapery sprigged with the same; round the festoones a twisting of white crape and silver rolls, with chord and tassels. Train, brown stain and silver fringe. Head-dress , silver crape satin, and white Ostrich plume.

Nothing very out of the ordinary in any of that. I think Isabella Thorpe's description of the hat in a Milsom Street window with "coquelicot ribbons" is a rare example of Austen using a rather fanciful name for a prosaic colour (red) and I suspect that it is supposed to tell us more about Isabella's pretentiousness, than suggest everyday usage.

I just had a quick skim through Evelina, but I can't find any mention of intriguing colour you talked about. On my next 'proper' re-read, I'll look out for it.