Do Herbal A and Herbal B correspond to differences in imagery?

[geoffreycaveney]

this page again suggests that red was a separate, final pass.

"Final pass" is a good idea.

I believe paint was rather expensive back then, what about comparative price of different colours? Was red more expensive than, say, blue?

I know very little about art history, but from what little I know, I agree with Koen, that red was always traditionally a more widely and readily available pigment colour, and also that blue was generally considered much rarer and more difficult and expensive to obtain. But again, this is just a general statement about paint colours throughout millennia of history, not any particular knowledge of the availability and expense of specific colours of paint in early 15th century Europe in particular.