In Irish 'dark', 'fair', 'black', 'brown', etc., often refer to the colour of someone's hair. Roisin Dubh, Eoghan Bán, etc. Many Irish names come from these descriptions - The first name Fionn, or the surname Dunne, for instance.
And, when referring to someone with black skin the word 'gorm' is used. Fear gorm - a blue man. The expression 'fear dubh' means the devil.
I always thought that was quite interesting, that in Irish black people are referred to as blue. I heard it is suspected either to come from having made the acquaintance the Berber or North African people, who tended to wear robes died with bright blue die, or perhaps from exposure to people from deep Africa who were so black that there was almost a bluish sheen to their skin.
There is also a tendancy for old norse (which did influence irish slightly) to describe things that are a dark colour or black as being blue (they did the same for red and yellow as well). One theory on the matter that i've found interesting is that they didn't have the tech to easily make a black dye, so dark blue was the closest they got to black. This then leading to blue and black being the same Very specifically, african men who appear in the norse sagas are described as 'blue men' as well.
No, "c" is a consonant, and "ch" is the lenited form of "c". Irish has epenthetic vowel, which is pronounced "uh". Epenthic vowels are inserted between a "r/l/n" and "c/g/p/b"