When you say pimpled shells I assume that you mean rough/bumpy shells. This can because by calcium or calcium to phosphorus imbalance. Also I think there are diseases that can cause rough shells. But this is probably not as likely as calcium or calcium to phosphorus imbalance.
I have heard/read that chickens eventually, after laying for awhile, start laying paler eggs because they started running out of the dye for their egg color. After a molt they replenish their stock.