As Sparks mentioned, in a FIRST robot, red is alway positive and black is always ground. In the past there have been rules governing this, and there probably will be again this year.
Anybody who has worked on a robot will tell you that the wiring can quickly become a mess and make things difficult to tell what's what. Something that we do (and I know other teams have done) is color code everything with colored tape. For example, if we choose green for a certain motor, we'll put green tape on everything that connects the RC to the motor. You will see tape in the following places
* RC pwm output
* PWM cable on both ends and in the middle
* Fan on top of speed controller
* Both wires coming out of speed controller to motor
* Motor itself
You will also see the same tape on all power paths to the speed controller
* Breaker panel
* Breaker
* Red/Black wires at both ends
This allows us to quickly determine which wires go where in the case that we have to get in there and work on things. Its a lot easier to ask somebody to trace the green wire than try and describe a certain red wire. We use part STD-C-ND available from Digikey. It's a little pricey, but well worth it. I've also seen some teams use labels from a labelmaker and stickers (I seem to remember Scooby Doo stickers
)