I've never had it on my car tyres but on my race bike on every outing after every session with either a new or used set of tyres I always had a blue oil ish looking colour on the tyres! I really wouldn't worry about it!
I had the 25mm spacers all round and my car was 'driven' pretty hard and and it made no difference IMO to the braking or handling of the car. It make the car look awesome!