diff --git a/contrib/python3-whitelist b/contrib/python3-whitelist
--- a/contrib/python3-whitelist
+++ b/contrib/python3-whitelist
@@ -124,6 +124,7 @@
 test-diff-antipatience.t
 test-diff-binary-file.t
 test-diff-change.t
+test-diff-color.t
 test-diff-copy-depth.t
 test-diff-hashes.t
 test-diff-ignore-whitespace.t
diff --git a/mercurial/patch.py b/mercurial/patch.py
--- a/mercurial/patch.py
+++ b/mercurial/patch.py
@@ -2480,7 +2480,7 @@
                 endspaces = chomp[len(token):]
             # scan tabs
             for maybetab in tabsplitter.findall(token):
-                if '\t' == maybetab[0]:
+                if b'\t' == maybetab[0:1]:
                     currentlabel = 'diff.tab'
                 else:
                     if changed: