I've had a theory for a long time that, character wise at least, each Doctor regenerates each time into something more like the guy the previous incarnation deep down wished he could be. E.g. the 1st got fed up with people finding him cranky, so he became the kindlier 2nd; The 2nd had to do an awful lot of running and had problems with being taken seriously (in the novelisation, he even mentions that at his trial!), so wished for a taller body with longer legs (of course that one was manipulated by the Time lords anyway); The 3rd died after having to face his fear: He wished to be a bit bolder and more carefree... The 4th was beginning to feel very old around all those young humans (he was *behaving* old as well, by then), so he becomes much younger... The 5th was constantly frustrated by not being able to be a very imposing presence, and also felt guilty about all the death that occurred around him while he tried so hard to the peace-maker, so he wanted a nice loud bellow and a thicker skin and a more gung ho attitude... The 6th realised he was blundering into things a bit too often and wished to be more of a thinker and planner... The 7th was tired of carrying the weight of reponsibility and wanted to be someone a bit more byronic and carefree... The 8th got caught up in a war that wiped out his own people, and (like the 5th, only more so) felt a desperate need for a tougher skin to get through life... And the 9th had been through his primary stages of grieving, and needed to leave that behind and open up more...

So maybe DT's Doctor is nursing a secret desire to be a cool black dude/dudette? =:o}