I'm not contradicting this as that is certainly what all the research I have read suggest, I just find it a little odd... At high noon, on a summer day, sea level, at the equator the light is give or take 6500K, that is the cool spectrum... The 3000K or so warm light is more so spring, fall, sunset, sunrise color... My guess is that the warm light is more so to trick them into thinking spring something would be their normal ancestral laying time...
As I said, I'm not arguing it I just find it odd being an indoor plant/flower grower... I (and many others) start all my seeds and young plants under 3000K light to simulate the early spring light conditions as as the plants grows I slowly transition them to pure 6500K light as that is beneficial for summer fruits/vegetable and flowering...
I start my plants under the same light conditions.
The warm light spectrum working better for chickens is what i read in this University of Maine Cooperative Extension Bulletin http://umaine.edu/publications/2227e/ It covers the lighting for all the stages of growth and gives pretty good explanations of why its is done. Its well worth bookmarking.