"La nuit est noire."
because in French you never pronounce the last letter. ( maybe there are exceptions not sure, but mainly it is not.)
la femme noire ( femme = female so you have to add a E at noire) le garçon noir ( garcon = male so you do not have to add a E. )
Noir says something about the Subject, and when the subject is female you add a E
I hope this is understandable :D