I have Aluminum wheels on my ZL1 and just checked all four rims. Mine are evenly painted in each lug nut recess. Sorry to hear of your experience. Wonder if this is a 2013 problem or all years.
For anyone having problems keeping rims clean, I highly recommend Armor All Wheel Protectant. You spray it on and let it dry > 1 hr. It will cut the brake dust down by an order of magnitude.