I have my own roller mill so I mix my own using Kent chicken minerals. I can a just protein and calcium levels as needed for any batch that I make and the corn is always ground fresh so the get the most out of the oils in it. I also throw in some sunflower seeds as a treat!
The dark yolk is from my chicken that had been eating my feed all winter. The other two were from a neighbor who feeds layena. All birds were penned for the winter and approx the same age and were at the beginning of their laying cycle late winter.
20% protein feed with oyster shells always free choice, and sometimes mixed in if I notice thinner shells. We get ours from a local mill so, even though it has GMO corn/wheat/soy, it is at least fresh and doesn't have to sit or travel very far after being milled. Not to mention high protein treats like sunflower seeds and meat scraps of all kinds.