You heated the rotors up. Totally normal
On the rotor surface, that looks like a very nice transfer layer/film from the pad.
Come join us at the track subforum here:
http://www.ft86club.com/forums/forumdisplay.php?f=39
And, please contribute to the (race) brake pad discussion here:
http://www.ft86club.com/forums/showthread.php?t=23680