From the 1610s, a compound of water + melon. The meanings referring 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.
2010 August 7, Robin McKie, “Merchants of Doubt by Naomi Oreskes and Erik M Conway”, in The Observer[1], →ISSN:
According to this distorted view of life, environmentalists are watermelons – green on the outside, red on the inside – who want to impose regulation, “the slippery slope to socialism”, on the use of tobacco, ozone-destroying chemicals and greenhouse gases.
A pinkish-red colour, like that of watermelon flesh (also called watermelon pink).
2011 August 8, Marc Löffler, “Watermelon Reporting”, in DZone[2], AnswerHub:
The nuts and bolts of any project are transparency. If the project status is transparent, the watermelons can’t arise. If anybody is able to get the information, it will be difficult to hide something.
2015 September 17, Ken Burrell, “Watch out for watermelons in project reports”, in LinkedIn[3]:
As a PMO [project management officer], wherever I see watermelon reporting, I encourage the PM [project manager] to be brave and honest enough to ask for help.
2021 April 24, Sumir Karayi, “Combatting the Watermelon Effect to Improve Digital Experience”, in CIO[4], IDG Communications, archived from the original on 5 June 2021:
