susan tuck

Does anyone know how to tell what color or how dark a sable dog will be when it is an adult? I've heard from some that they don't get their true color until they are 3 years old. I've also heard that they end up being similar to what they were as newborns. One thing I have found out is they sure change color a lot. Arkane can be nice & dark for a while, then I get worried because it looks like I have a yellow dog, then he darkens up again. The black penciling has remained all the way down his front legs & on his toes, and his hocks are black. Is there any rule of thumb?
I've always had black & reds in the past.