"Blueing" of tires? symptom of racing? bad, good or not affecting value?

The guy may just drive it hard. What's he telling you? If you look at the overall condition and the car checks out then it shouldn't really be a problem. What you see should be consitent with what you're being told both verbally and through mileage etc.

 

I run those tires but never noticed anything like that...fine tires.

Somtimes I've seen wonky tire dressings turn off color like that......

 

Blue-ing is a symptom of a severe heat cycle. Most likely it is due to a track day or something. It could be that the tire pressure was too high for a long(er) spirited drive somewhere. I have only seen severe blueing on my race take-offs after they are Well spent.

Edit: Looking at those tires again, I wouldn't be too worried. The blueing does not reach to the side wall at all. At a track day, the tires are flexed, twisted and pushed to their absolute limits in most cases and the blueing is very severe and reaches beyond the tread face. If anything I would think that the person ran the car with in-correct tire pressure. Too high or perhaps too lowcausing that portion of the tread to heat up more than the rest. Just MHO.