Norihiro Tanaka <noritnk@kcn.ne.jp> writes:

> On Mon, 16 Mar 2015 08:49:29 +0900
> Norihiro Tanaka <noritnk@kcn.ne.jp> wrote:
>
>> AUTO and ALWAYS are POSIX incompatible,
>
> In addition, if the default is AUTO, and they are also imcompatible with
> previous versions of DIFF by default.

I meant the default if --color is specified.  That is not incompatible
with any previous version since --color was not present.

Apparently, ls and grep already behaves differently for --color so diff
is not going to make any other difference here.  "ls --color" means "ls
--color=always" while "grep --color" behaves like "grep --color=auto".
Having to choose between these two, --color=auto makes more sense for
diff where redirection to files is a common operation.

I am attaching the latest version of the patch, taking into account
comments from Andreas.  I have added colors for header and line numbers,
following the "git diff" colors scheme.

Thanks,
Giuseppe