So, if I were to add cosmetic battery powered LED lights to my robot, and the ambient light from the lights just so happened to accidentally give a vision sensor on the robot enough light to make a reliable and accurate reading on the color of a ball, would the lights still be allowed?
Sadly, no. In that case the lights would be a functional decoration, and therefore not allowed. However, the new optical sensor has its own flashlight and therefore should be much better at sensing the color of balls.
Could you get away with it? Probably. Should you just buy the optical sensor instead? Yeah.
That’s actually a pretty clever idea. You essentially want the same function as the Optical Sensor like 2775Josh mentioned above. Unfortunately the Optical Sensor is out of stock at the moment.
But the VEX Flashlight isn’t! Flashlight - VEX Robotics
While currently using an LED light strip is considered illegal via R13g, the flashlight is legal to use for the same purpose that you described. Just be careful not to violate R13e if you do decide to give the flashlight method a try.