Color: Remember the papers and inbox-metaphor above? Color is the things you scribble on the individual piece of paper. Colored Petri Nets associate attributes with the individual token. This is something you often want to do in real-world workflows, i.e., people do scribble things on the papers in the inbox-metaphor, and it adds to the expression power of the workflow. It is commonly used in network protocol simulation and, of course, mathematically well-founded.