The colours increase the grieve amtosphere a lot. And I like how emotional they make this look. Simple lines, simple colours (just the grey scale), simple shading and a simple gesture are a proof that simplicity is one of the best ways of expressing strong emotions.^^
I like how soothing and worried at the same time the dog looks - like he was the girl's real (and maybe the only as well...) friend.
Wherever you got your idea from, it's a great idea. And the way you made it be an illustration is as good, if not even better. Great job!