diff --git a/mercurial/cmdutil.py b/mercurial/cmdutil.py
--- a/mercurial/cmdutil.py
+++ b/mercurial/cmdutil.py
@@ -627,7 +627,7 @@ def diffordiffstat(ui, repo, diffopts, n
                 # subpath. The best we can do is to ignore it.
                 tempnode2 = None
             submatch = matchmod.narrowmatcher(subpath, match)
-            sub.diff(diffopts, tempnode2, submatch, changes=changes,
+            sub.diff(ui, diffopts, tempnode2, submatch, changes=changes,
                      stat=stat, fp=fp, prefix=prefix)
 
 class changeset_printer(object):
diff --git a/mercurial/subrepo.py b/mercurial/subrepo.py
--- a/mercurial/subrepo.py
+++ b/mercurial/subrepo.py
@@ -330,7 +330,7 @@ class abstractsubrepo(object):
     def status(self, rev2, **opts):
         return [], [], [], [], [], [], []
 
-    def diff(self, diffopts, node2, match, prefix, **opts):
+    def diff(self, ui, diffopts, node2, match, prefix, **opts):
         pass
 
     def outgoing(self, ui, dest, opts):
@@ -437,14 +437,14 @@ class hgsubrepo(abstractsubrepo):
                                % (inst, subrelpath(self)))
             return [], [], [], [], [], [], []
 
-    def diff(self, diffopts, node2, match, prefix, **opts):
+    def diff(self, ui, diffopts, node2, match, prefix, **opts):
         try:
             node1 = node.bin(self._state[1])
             # We currently expect node2 to come from substate and be
             # in hex format
             if node2 is not None:
                 node2 = node.bin(node2)
-            cmdutil.diffordiffstat(self._repo.ui, self._repo, diffopts,
+            cmdutil.diffordiffstat(ui, self._repo, diffopts,
                                    node1, node2, match,
                                    prefix=os.path.join(prefix, self._path),
                                    listsubrepos=True, **opts)
diff --git a/tests/test-diff-color.t b/tests/test-diff-color.t
--- a/tests/test-diff-color.t
+++ b/tests/test-diff-color.t
@@ -125,6 +125,38 @@ qrecord
    c
   \x1b[0;33mrecord this change to 'a'? [Ynesfdaq?]\x1b[0m  (esc)
 
+  $ hg qpop -a
+  popping patch
+  patch queue now empty
+
 #endif
 
+issue3712: test colorization of subrepo diff
+
+  $ hg init sub
+  $ echo b > sub/b
+  $ hg -R sub commit -Am 'create sub'
+  adding b
+  $ echo 'sub = sub' > .hgsub
+  $ hg add .hgsub
+  $ hg commit -m 'add subrepo sub'
+  $ echo aa >> a
+  $ echo bb >> sub/b
+
+  $ hg diff --color=always -S
+  \x1b[0;1mdiff --git a/a b/a\x1b[0m (esc)
+  \x1b[0;31;1m--- a/a\x1b[0m (esc)
+  \x1b[0;32;1m+++ b/a\x1b[0m (esc)
+  \x1b[0;35m@@ -7,3 +7,4 @@\x1b[0m (esc)
+   a
+   c
+   c
+  \x1b[0;32m+aa\x1b[0m (esc)
+  \x1b[0;1mdiff --git a/sub/b b/sub/b\x1b[0m (esc)
+  \x1b[0;31;1m--- a/sub/b\x1b[0m (esc)
+  \x1b[0;32;1m+++ b/sub/b\x1b[0m (esc)
+  \x1b[0;35m@@ -1,1 +1,2 @@\x1b[0m (esc)
+   b
+  \x1b[0;32m+bb\x1b[0m (esc)
+
   $ cd ..