Object Modeling in Color
UML color standards are a set of four colors associated with Unified Modeling Language (UML) diagrams. The coloring system indicates which of several archetypes apply to the UML object. UML typically identifies a stereotype with a bracketed comment for each object identifying whether it is a class, interface, etc.
These colors were first suggested by Peter Coad, Eric Lefebvre, and Jeff De Luca in a series of articles in The Coad Letter, and later published in their book Java Modeling In Color With UML.
Over hundreds of domain models, it became clear that four major "types" of classes appeared again and again, though they had different names in different domains. After much discussion, these were termed archetypes, which is meant to convey that the classes of a given archetype follow more or less the same form. That is, attributes, methods, associations, and interfaces are fairly similar among classes of a given archetype.
When attempting to classify a given domain class, one typically asks about the color standards in this order: