%C(auto) not working as expected

[Tom Hale]

$ ~/repo/git/git --version
git version 2.10.0.GIT

The `git-log` man page says:
`auto` alone (i.e.  %C(auto)) will turn on auto coloring on the next 
placeholders until the color is switched again.

In this example:

http://i.imgur.com/y3yLxk7.png

I turn on auto colouring for green, but it seems that this is not being 
respected when piped through `cat`.

Am I misunderstanding the manual?

--
Tom Hale