The side of Minnietrost, one of the summer cottages, in winter sunlight. It was quite a struggle to decide on the color when they were repainted a few years ago. Appropriately, for the genealogists amongst us, it is Webster Green, a nice subtle grey/green. Winter light always has a sharper air to it, as if looking through glass rather than water.
(yes that is an iron strap holding the chimney in place…no it is definitely not usable at the moment! someday?)
Acair Fearann 
Lower humidity?? Not always the case, I know, but usually? Combination effect of temperature and humidity? Anyway, yes, winter air is sharply clear.
If I could find it (I know where it is generally, but not to put a finger on) I should send you for comparison the Christmas day photo of Minnetrost taken by me with my first real camera (Voigtlander, not Brownie) in, h’m, 1959?). Some subtle differences (if was cloudy, if nothing else!).