This was my first project using Processing. It was done for an excellent online class by Joshua Davis (Programming Graphics I: Introduction to Generative Art).
A grid of squares was generated using Processing. The randomness of colors in the final pattern was controlled by a greyscale repeatable pattern.
Another variation using a different initial pattern.
The possibilities are endless. These examples use a grid of squares. But, it could be any shape. The greyscale image could be used to control about anything beside color: scale, rotation, ….