diff --git a/aider/commands.py b/aider/commands.py
index bd2fb274b..94af9e380 100644
--- a/aider/commands.py
+++ b/aider/commands.py
@@ -477,9 +477,9 @@ class Commands:
             return
 
         if len(self.coder.commit_before_message) < 2:
-            return
-
-        commit_before_message = self.coder.commit_before_message[-2]
+            commit_before_message = current_head + "^"
+        else:
+            commit_before_message = self.coder.commit_before_message[-2]
 
         if not commit_before_message or commit_before_message == current_head:
             self.io.tool_error("No changes to display since the last message.")
diff --git a/aider/repo.py b/aider/repo.py
index cefb12fca..45857c1d4 100644
--- a/aider/repo.py
+++ b/aider/repo.py
@@ -227,6 +227,8 @@ class GitRepo:
         args = []
         if pretty:
             args += ["--color"]
+        else:
+            args += ["--color=never"]
 
         args += [from_commit, to_commit]
         diffs = self.repo.git.diff(*args)
diff --git a/tests/basic/test_commands.py b/tests/basic/test_commands.py
index 4cffd4043..c981418ea 100644
--- a/tests/basic/test_commands.py
+++ b/tests/basic/test_commands.py
@@ -818,7 +818,7 @@ class TestCommands(TestCase):
 
             # Mock repo.get_commit_message to return a canned commit message
             with mock.patch.object(
-                repo, "get_commit_message", return_value="Canned commit message"
+                coder.repo, "get_commit_message", return_value="Canned commit message"
             ):
                 # Run cmd_commit
                 commands.cmd_commit()