At least you know it isn't one of the Easter Eggers so that cuts the possibilities a bit.One of my girls has started laying a white egg...not sure what's going on & I don't know which one it is!
Laying has little to do with heat and a lot to do with the amount of light. They cut off when the hours of daylight grow slim and start back up when there is more light. That is why some people provide light in the coop (presumably 14 hours) in the winter if they want to force the girls to keep laying.Btw, I know birds up here in NJ slow down and stop laying in the winter. But what about down south where it's warm? Do the ladies ever get a break.....?