Yay for cotton coats! It's great to see so many of them. When I got Molli as a puppy I had no idea her coat was diffrent, from what I gathered I don't think you can really tell if they are a cotton coat until after 6 months old because before then they still have a puppy coat which is often fluffier than normal. As far as I know I think the hair is always black, I think it may lighten a litte (Molli's seems lighter near her legs) but it will never turn the "blue" color it is supposed to. I have two uniquely colored yorkies now so I am loving it.The matting up is hard to deal with sometimes but I keep her short most of the year and use a detangler on her. Small price to pay to have your dog look like a puppy forever
Here is a pic of Molli as a baby and then one of what she looks like now (she just turned 2yrs)