The latest word from Moffat about what Capaldi's Doctor will be like:
"Now we're going to give her a Doctor who's not like that at all [The Eleventh Doctor], who's a much older, fiercer, madder, less reliable Doctor, who leads her a merry dance. And she's trying to keep him a secret and she's now working in a school..."
On The Twelfth Doctor's character, Moffat comments that he will be more akin to Tom Baker and Christophe Eccleston, being "mad and dangerous and difficult" and not a "quirky young man" like Matt Smith and David Tennant.
Sounds more like Colin Baker than Tom, from that description.