There is a biography, Colt & Co. by Fred Hawtree a member of the Hawtree line of british architects. I believe it is out of print. It has a wonderful section at the back in which correspondence among Colt, Allison, and Morrison is reprinted. There is also some real detail about Colt's method of work (eg use of plasticene models of greens) but not much on strategic considerations. It has been some time since I pulled it down from the shelves but as I recall it was not the easiest read although, given that it is the only biography extant, it was somewhat informative.