Pass color option to git diff unconditionally

pre_commit/commands/run.py

@@ -224,13 +224,10 @@ def _run_hooks(config, hooks, args, environ):
                 '`pre-commit install`.',
             )
         output.write_line('All changes made by hooks:')
-        if args.color:
-            subprocess.call((
-                'git', '--no-pager', 'diff', '--no-ext-diff',
-                '--color={}'.format(args.color),
-            ))
-        else:
-            subprocess.call(('git', '--no-pager', 'diff', '--no-ext-diff'))
+        subprocess.call((
+            'git', '--no-pager', 'diff', '--no-ext-diff',
+            '--color={}'.format(args.color),
+        ))
 
     return retval
 

tests/commands/run_test.py

@@ -181,12 +181,6 @@ def test_global_exclude(cap_out, store, tempdir_factory):
 @pytest.mark.parametrize(
     ('args', 'expected_out'),
     [
-        (
-            {
-                'show_diff_on_failure': True,
-            },
-            b'All changes made by hooks:',
-        ),
         (
             {
                 'show_diff_on_failure': True,
@@ -198,6 +192,7 @@ def test_global_exclude(cap_out, store, tempdir_factory):
             {
                 'show_diff_on_failure': True,
                 'all_files': True,
+                'color': 'auto',
             },
             b'reproduce locally with: pre-commit run --all-files',
         ),