I would like to know if anyone understands the reason that the so-called "golden/aurea" cultivars of pines, spruces, junipers, etc. turn yellow in the winter and then green in the spring/summer/fall? I assume that the chlorophyll in their needles dies off in cold weather and shows an underlying yellow pigment. This yellow pigment is obscured in the spring when the weather warms and the tree becomes physiologically active. Has anyone studied this in detail?