Missing color legend on pinout image S2 Mini

[DavidMR91]

What does the color legend of the documentation image mean? https://www.wemos.cc/en/latest/_images/s2_mini_v1.0.0_4_16x9.jpg

[R-S-M-A-N]

Hello, I am a beginner and I too wonder why there is a color difference? If anyone has the answer I'm curious to learn!