Fern was a shade of green named after a certain plant.
The Eighth Doctor wore fern green trousers when he witnessed C'rizz's death on Utebbadon-Tarria. (AUDIO: Absolution)
Missy, a feminine version of the Master, wore a fern brocade cravat; (TV: Extremis) right up to her fall after being shot by her predecessor with a laser screwdriver to stop her from helping the Twelfth Doctor to save Mondasians from Exodus Cybermen. (TV: The Doctor Falls)