is this a bug in blender?

I made a simple car and later made two headlights in front. I made the car red and the head light yellow, then I joined the headlights to the car. Afterwards I boolean the cab of the car and I hit applyed, the whole car and the headlights turn red, but then I redid the car and headlights, but this time I did not join the lights to the body of the car, so when I boolean the cab, the lights stayed yellow and not red, is this normal?