I’ve found a new source for the colour in “The Colour out of Space”, on which more in my forthcoming review of Lovecraft Annual 2020. In the meanwhile, those fascinated with the histories of colour may be interested in the latest shelf-trembler from Bloomsbury. The mammoth A Cultural History of Color runs to six handsome volumes, and costs £395. Which I think is roughly about $500.
A pity, perhaps, that there wasn’t also a pre-history volume surveying and summarising what we now know about colour in the deep past. Although, admittedly, the emphasis might have been largely on the various shades of ochre and umber.