Amazing replies and links - thanks all!
She seems to be wearing a little hat made of feathers - Robert Place either overlooked it or chose to disregard it in his digital painting. I'm wondering if it could give a clue as to the colour of her dress, because from what I know of antique feather hats the feathers are unlikely to be blue (due to rarity), and are too dark for yellow, pink, cream etc.
In the UK the most common feathers used for hats were (I think!) pheasant feathers, which were shades of brown/orange, and striped, spotted and patterned in a variety of ways, depending on where on the pheasant they came from and whether the bird was male or female.
There's a similar smaller one to Pamela's headpiece (except for the patterned feathers!)
Here, but a search is interesting too.
I'm pretty sure that the lacy (beaded?) appliques would have been black.
I mention the hat because (especially) as an artist she'd be aware of the importance of colours, even if she chose not to harmonize/co-ordinate. And of course she was a natural Bohemian...
And then there's that letter re. her dress sense - deeper and deeper we go...
Pen