How fun! interesting that it would be two days in a row. The yellow may just be a way to make sure you know this dog is different than the one you all ready have. Could this dog be someone who was once in your life, a mentor, parent (older and wiser you said) who has since passed on?
naturally you will have your own associations for what dogs mean to you, but in general they stand for loyal companions who love us unconditionally. And if you take the perspective that everyone and everythign in a dream is an aspect of you, then this dog is representing the part of you that is wise, loving, old because our souls are old or at least beyond linear time. So you're getting a glimpse of a part of your psyche that perhaps you don't acknowledge enough in your waking life.