Yes, completely normal. Throughout the winter, depending on the thickness of the coat, the hair should appear darker. My horse is a bay, and has lighter points around his muzzle, but when his winter coat is in full bloom, he's one solid color. Once that coat sheds, or if bleaching occurs, their coat should change once more.
Yes it is completely normal! Horses go through many different coats. As they shed out their winter coat and their summer coat grows it could be different lengths and colours. Also if you have a dark horse they tend to get bleached by the sun. My horses change colour too. My bay horse gets brighter in the summer and my buckskin gets brighter as well, mostly from the sun. I find putting a fly sheet in them helps protect them from the sun bleaching.