Higher producing hens especially will have less pigment to deposit on each egg shell as their season progresses, it's normal. And egg size may vary a bit, even day to day.
Layer feed is designed for leghorn type birds in confinement, with no other foods offered. It's perfectly balanced for those birds, and easy to unbalance when anything else is added, and for bigger breed types.
Some of us do feed a higher protein diet, usually an all flock diet that's 18% or 20% protein, with oyster shell in a separate dish. Then anything in addition is less likely to cause deficiencies, very helpful. And extras should be a small part of their diet, usually described as no more that 10%.
Also, make sure each bag of feed is fresh! I use mine up within two months of the mill date on each bag. Always. Some vitamins don't last a long time, and stores will sell older feed often.
Mary