There was a thread on here somewhere that talked about how chickens need a LOT more protein than we usually give them to lay decent eggs and stay healthy, too. Grubs. Mealworms. ALL that stuff.
About your multicolored yolks -- I read how the chicken builds the yolk in layers (no pun intended!). Layer after layer is added as the yolk goes down the channel, and the shell is added in layers, too.
Maybe the multicolored yolks you've been getting are showing the changes in the chickens' diet. (?????) It seems logical to me. But then. . . .I've heard from some people who say I'm not always the most logical person they've ever met. I'm thinking they're all blind, though.