The keep colours
The keep colours refer to the rough colour and positioning of the pressure-sensitive puzzles from The Keep area in The Witness. According to Jonathan Blow, these colours have meaning, but no one has figured out what they could mean. <Insert video where Jon says they have meaning.>
Aside from The Keep, the colours have been spotted under The Mountain, in Braid, and on Froot Loop boxes.
These colours are the origin of the Witscord logo.