The Fennas word for blue is plas. Plas is a last name. In Breton plas means place. In Welsh plas means hall, mansion. In Dutch and Danish plas means lake. Plas is the name of a city in Belgium.
In Welsh and Breton the word for blue is glas. The Irish word for blue is gorm.
Yes, I know that the Celtic words start with G. I decided to make my Fennas word for blue similar but different.
The Fennas word for the color black is duth. Duth is a last name. Duth seems to be a misspelling of doth which is an archaic English form of does.
My word, duth, seems a reasonable word for black, maybe because it's similar to the word dusk. In Welsh and Breton the word for black is du. The Irish the word for black is dubh.