Vex u sensor clarification

Would it be considered illegal in Vex U if a sensor was used to detect a tshirt color outside the ring?

Depends on the application…

Accidentally picking up surrounding colors from a poor sensor mounting is possible, but intentionally interacting with the robot by sending it signals during autonomous is definitely illegal. This would include something like showing it a “green” object to turn one way, and a “blue” object to turn another.