Hello,
Welcome to forum.
Some resources to add to this topic for all:
https://processing.org/tutorials/color/
https://processing.org/examples/colorvariables.html
https://processing.org/reference/color_.html
https://processing.org/reference/ See color. 
Its insightful to peruse the source but not always easy to find what you are looking for.
Some of the Processing functions here:
Processing source code - PApplet.java
Doing a search for “color(” for example narrows down the search and can be done for other functions.
:)