Ok, so this happens every time I go to the track, and this past weekend I took note that it happens to my bike only.
I'm guessing it's simply impurities in the cheap Arashi rotors discolouring, but figured I'd ask if anyone's familiar with this? I redid my brakes entirely last August; new seals and pistons and I've checked to ensure they're still retracting properly, and I'm running Vesrah RJL pads.
The brakes still work fine; in fact they seem a bit better once the pads have warmed up after a couple laps... but I'm curious about this discolouration and if it's something to be aware of ie. it being indicative of cheap steel and thus more likely to crack or anything.