We found another book that mentions Pimlico Ale, which I spoke about in this post a few days ago.
William Carey, in his weird, limited edition history of the area, published in 1986, writes:
The most popular ale drunk in London between 1570 and 1700 was ‘Pimlico Ale’ otherwise known as ‘Derby Red Cap’ from the pink tinge of its frothy head. At first produced only in Derbyshire at a farm location named “Pimlico”, it was brought to London in huge barrels down the Watling Way.
This is very interesting. What makes the head pink/red? Fruit could, but the head on some imperial stouts is reddish brown. More research needed – in books on Derbyshire, perhaps…?