Blue = lights are on or off
Green = Pit line limiter
Yellow = Hazard/indicator lights
Edit: from what i know it is a new feature for the new patch because in patch Z the lights are in a different order but in 0.6A the lights are rearranged to handbrake, Not sure, rev limiter, lights, pit limiter, Hazard/indicator lights.
Edit 2: from what i can tell the xrr has an oil light warning so i am guessing it could be for that.