BLACK

Colours, in French, have to agree with the noun they describe.
All nouns, in French, are either MASCULINE or FEMININE.
Each colour is written twice.
The BLUE writing is the version used to describe MASCULINE nouns.
The RED writing is the version used to describe FEMININE nouns.
For some colours the masculine and feminine versions are the same.

DON'T FORGET THAT, IN FRENCH, THE COLOURS COME AFTER THE NOUN