Pinkies with yellow dots? Help?

i just went to feed my corn snake and noticed as it was defrosting it was covered in yellow spots :S i looked at the other pinkies a have and they all seem to have some spots. It didn't look right so haven't feed any of them to him. i bought them nearly 2 weeks ago they have been in the freezer ever since, the 2 i have already used didn't have the spots. Whats wrong with them??