color: fix colorization of the 'old mode' git diff metadata

hgext/color.py

@@ -204,6 +204,7 b' def colordiff(orig, ui, repo, *pats, **o'
 _diff_prefixes = [('diff', 'diffline'),
                   ('copy', 'extended'),
                   ('rename', 'extended'),
+                  ('old', 'extended'),
                   ('new', 'extended'),
                   ('deleted', 'extended'),
                   ('---', 'file_a'),