Easter Eggs are intentional inside joke or hidden features of the game.
As walt writes:
The satisfaction that comes from finding the secret coconut is the greatest reward of all!
The Hidden Coconut
The Hidden Coconut was walt's reaction to ArticHawk's post in request of the addition of coconuts, and was added in Cosmoteer 0.12.12. It is found on all of the floor sprites of the Control Room, but is only visible in-game when the control room is at 66% damage (since 0.13.0. Prior, was completely hidden by the doodads layer at all times). In the 0.13.0 Multiplayer Update, the coconut's position on the floor was changed in the 66% damage sprite, so that it could be seen ingame. As quoted in the changelog:
The secret coconut is now 15% less secret
The Retro Mode idea came up from a discussion about jamming sensors and combining it with measures against piracy of Cosmoteer. It was "subtly" introduced in the Cosmoteer Release Candidate 0.14.2rc1's patch notes, as quoted by Walt:
Whatever you do, DO NOT PRESS SHIFT+TILDE+8.
Pressing Shift + Tilde (~) + 8 will overlay a shader on the game which changes all colors to green, and reduces the screen resolution. The shader file is named "8bitmode.shader" and can be easily found in the game files.