Watermelon

wiktionary

ref

From the 1610s, a compound of water +‎ melon. The meanings refering to environmentalists and behind schedule projects derive from the idea of having green (eco-friendly, on-schedule) outward-appearance while being red (socialist, behind schedule) in a hidden way comparable to that of the fruit.

etymonline

ref

watermelon (n.)

1610s, from water (n.1) + melon. So called for being full of thin juice. Compare French melon d'eau.