Your rear Drums are painted similar to my front drums on your 1971 Challenger. Mine are painted right and including the cap. The red paint looks great with the 5 spoke wheels. Likely there is no reason why Chrysler choose the red. The only reason is to tell a worker these were Rallye or Five Spoke Wheels on this E Body but that is what a line spec sheet it for to make sure each Vehicle is getting the correct wheels. But If someone follow all the paper work through out the plant there should not be a loading mistake on each line but we are all Human. I still think Black would of been a better color for all types of rims. Red must of been a Key for the line workers but if the line worker misses painting the drum then what happened.