Meant to add this to the book review: despite the depiction of Sebastian Dangerfield on a couple of the various covers that various editions of The Ginger Man have carried over the years (see below, for instance) there's no suggestion in the book that the title is meant to refer to Dangerfield's hair colour. I mean, he might be one of the gingers, but as far as I recall it's never mentioned.
Instead I read the title as either referring to the fairy tale The Gingerbread Man - "run, run, as fast as you can; you can't catch me, I'm the gingerbread man", or possibly as referring to ginger in the sense of lively, zesty, as per definitions 4 and 7 here. This usage derives from the practice of "gingering" a horse to liven it up by shoving a piece of raw ginger up its arse. I don't think this is a thing unique to horses, as it happens, since I'm pretty sure I'd react in a similar way. And sure enough there is a (one hopes) consensual BDSM sex practice called figging which involves pretty much the same thing.