Black -> grey -> white with easing

Do someone know how to do so a movieclip intancename example would first be black (witch it is right now) to darkgrey, then grey, then lightgrey then white? (this is just example colour, It shall work with other colors as well.)
And I also wants that if you write duration = 30; it vill last in 30 frames.
please help me, I have seached in a hour now after this (but I am not an expert on searching ;))