This photo reminds me of the golden rule. Horses engage in a mutual grooming behavior where they stand beside each other as these foals are and scratch each other's backs or withers with their teeth. The foal at the back doesn't look totally happy, so that might not be what they are doing. :)
Also, when young, foals have a very soft, fuzzy coat. That coat sheds out as they get older and is replaced with hair that is sleeker and more horse-like. It's not uncommon for the new hair to be a different color than the foal coat. The new hair tends to come in slowly and in different areas at different times, so the foals often look very unusual. Both of these foals are starting to get their "adult" hair around their muzzles and eyes.