Yesterday for some reason I thought of the word "redden" - go red or make redder - which set me to wondering if there are similar words involving other colours. "Blacken and whiten" came readily to mind but when I thought about "bluen" for example it didn't feel right, I wasn't sure there was such a word.
So I searched, using the 11 basic English colour names, first in the OED and then if a word was not there, in Wiktionary, and turned up several more.
Redden OED
Blacken OED
Whiten OED
Greenen not found
Yellowen Wiktionary
Bluen Wiktionary
Brownen not found
Pinken OED
Greyen Wiktionary
Purplen not found
Orangen not found
There is a large literature that deals with the order in which colour names might have evolved and I wondered at first if the colours with and without -en compounds might reflect that in some way. Then a different explanation occurred to me. Here from ResearchGate is a chart of the frequencies with which the colour names are found, taken from Google n-grams. [1]
Apart from the rather surprising "pinken" there seems to be a clear pattern. The words I thought of first correspond to the commonest terms; the others I found corresponded to the moderately common terms, except green and brown, presumably because "greenen" and "brownen" are awkward words to say*; and the rarer words don't have an -en compound.
This raises an intriguing possibility; if we come across a few odd fragments of writing from the ancient civilisation of Fantasia and were by some miracle able to identify and translate a handful colour words, the chances of the terms for red, black and white occurring would be high, while orange, pink and purple would be unlikely. We might conclude, quite erroneously, that the ancient Fantasians had no word for purple, or even that they couldn't distinguish purple from blue.
* In contract to -en compounds we can add -ish to any colour we like and come up with a word that feels perfectly reasonable, for example turquoiseish or heliotopeish.