What do the colored lines on the rear view camera represent on my 2017 forester

Refer to the manual and it should have all the information needed regarding the back up camera.

They represent different distances. I think the red ones are the danger zone where you could back into something.

Represent? That you're not colorblind, for one. Try to close in on the red ones often so that you can develop a relationship with your insurance agent. Then maybe read the manual?

This is one of a couple of things that I've already discovered aren't addressed in the driver's manual for our Subaru (another being how to turn off the radio so that it doesn't come back on again when you restart the engine). Based on what I've seen so far, the voluminous amount of information that Subaru provides on features we'll never used didn't leave the driver's manual developers enough time and space to cover "everyday" topics.