Seems okay functionally, but code isn't very understandable (quite a few magic numbers) and I'd be cautious to include code I don't understand. <s>It's definitely editing code at the wrong place though — the action for `--nocolor` apparently has to be `store_false`; otherwise, if your `use_colors` happen to be false, `--nocolor` would actually enable color. So the PR needs a medium rewrite anyway.</s>
Since you don't want to spend more time on this, I guess I'll rewrite it later while cross referencing colorama's win32 implementation. A brief look tells me that you might have only modified stdout (where the magic number -11 comes from) but not stderr.