Use of “marron”

Question

My dictionary shows both feminine and plural forms? Notes suggest that “marron”doesn’t change. Please explain.
Jan Gannon

Maarten Kamp · Accepted Answer

The lesson is specifically about the use of 'marron' as an adjective for a colour - in this context it is invariable as stated. 
There are other meanings for 'marron' as a noun or adjective, and it can be variable in those contexts, although use in the feminine form is rare, according to Larousse.
 https://dictionnaire.lerobert.com/definition/marron 
https://www.larousse.fr/dictionnaires/francais/marron/49608

Sophie David-Gunn · Answer

here is an easy answer for you (I hope!) Marron is a nut. Noisette is also a nut. They are nouns and used as adjectives for color. (from a French native teacher)

Maarten Kamp · Answer

However, marron has meaning beyond just being a nut, or a colour. Hence the dictionary links.