Some of the horses change color dramatically as they get their winter coats. I'll have to take some pictures so we can compare them with the photos I took in August for my Horses Are the Color of Earth post. Dawn, who has a very red summer coat, gets much darker in the winter. Maisie and Sugar, who are both dark bays - Sugar much darker - do get somewhat darker as well. But then Noble, Joe and Charisma, who also have red coats in the summer, don't really change color all that much. This must result from variations in the black genes that cause them to be bay. Our two buckskins, Misty and Scout, get slightly darker, more golden, and Misty loses her "frosting". The horses with pronounced dapples, especially Maisie and Sugar, who have whole-body dappling, lose their dapples, although last winter Maisie kept some of hers.
Since our barn is unheated, and the temperature gets as low as 10F in there on the coldest days - when it is below zero outside - it's good that our horses get good coats. Good health and good nutrition really determine coat quality - a horse with a poor coat likely has something wrong. We do put on rain sheets when the temperatures will be in the 50s or below, but we don't have to use heavy blankets all that often. When we do blanket, it's as much for wind as cold, since our winter dry lots (as well as our pastures) have no shelter to speak of. Our horses also have access to free choice round bale hay in the winter months, so digestion can help keep them warm. We do have a couple of horses who get cold more easily - Joe, Noble and Blackjack due to their age and Noble's thinish coat - and our "fragile flower" Dawn, who often wears her heavy blanket outside - a heavyweight Rambo with a full neck - and even inside in the coldest weather. She also has a polarfleece cooler for nights that aren't cold enough for her heavy blanket.
It's seeming much more like fall out there - darker in the mornings and more cloudy with a little rain on and off, and the trees are losing their leaves. Winter's not far away.