Yellow as in the OEM license plate lights, in order to match the untouched (non-camera) light. As about LEDs, I am not a huge fan, they might look nice on E60 and friskier models, but the old E53 looks ok with OEM lights. But like everything else, it's just a matter of taste, everybody fitting on his/her car what he/she considers best.
I was just thinking of an easy fix for the new camera fit, where the camera comes with LED and you have to match the two lights (left and right) together. You can either dim the LED, or upgrade the other one to LED too.