2D entities are colored to indicate their constraint status. The colors will help you to identify sketch entities that may require constraints or are in error. There are five colors used to denote the status of a 2D entity:
Teal: Under-constrained
Blue: Well Defined
Black: Fixed
Red: Over-Constrained
Gray: Inconsistent or Unknown
Note that fixed plane edges are drawn as dotted black lines.
Other Sketches and Planes topics: