Yellow tire smoke

I was doing burnouts and noticed that the smoke coming from the tires was yellow,is this a bug or something?

Proof picture (even without the filters the smoke was already very yellow):

PS: This only happened to me in the Airport Test Track.

Probably just dust/dirt. You get dirt show up if you do a burnout in the sand/grass.

There isn’t any dirt on the Airfield track. Must be a glitch

I think that’s just dirty, old concrete.

I think they used dirt / sand due to it being in the desert and sand blows around like crazy out there.