diff --git a/tests/basic/test_io.py b/tests/basic/test_io.py
index 3f313219d..93befabec 100644
--- a/tests/basic/test_io.py
+++ b/tests/basic/test_io.py
@@ -33,6 +33,43 @@ class TestInputOutput(unittest.TestCase):
         with patch.dict(os.environ, {"NO_COLOR": "1"}):
             io = InputOutput(fancy_input=False)
             self.assertFalse(io.pretty)
+            
+    def test_color_initialization(self):
+        """Test that color values are properly initialized with # prefix"""
+        # Test with hex colors without #
+        io = InputOutput(
+            user_input_color="00cc00",
+            tool_error_color="FF2222",
+            tool_warning_color="FFA500",
+            assistant_output_color="0088ff",
+            pretty=True
+        )
+        
+        # Check that # was added to hex colors
+        self.assertEqual(io.user_input_color, "#00cc00")
+        self.assertEqual(io.tool_error_color, "#FF2222")
+        self.assertEqual(io.tool_warning_color, "#FFA500")  # Already had #
+        self.assertEqual(io.assistant_output_color, "#0088ff")
+        
+        # Test with named colors (should be unchanged)
+        io = InputOutput(
+            user_input_color="blue",
+            tool_error_color="red",
+            pretty=True
+        )
+        
+        self.assertEqual(io.user_input_color, "blue")
+        self.assertEqual(io.tool_error_color, "red")
+        
+        # Test with pretty=False (should not modify colors)
+        io = InputOutput(
+            user_input_color="00cc00",
+            tool_error_color="FF2222",
+            pretty=False
+        )
+        
+        self.assertIsNone(io.user_input_color)
+        self.assertIsNone(io.tool_error_color)
 
     def test_dumb_terminal(self):
         with patch.dict(os.environ, {"TERM": "dumb"}):
@@ -392,6 +429,31 @@ class TestInputOutputMultilineMode(unittest.TestCase):
         # Test prompt_ask()
         io.prompt_ask("Test prompt?")
         self.assertTrue(io.multiline_mode)  # Should be restored
+        
+    def test_ensure_hash_prefix(self):
+        """Test that ensure_hash_prefix correctly adds # to valid hex colors"""
+        from aider.io import ensure_hash_prefix
+        
+        # Test valid hex colors without #
+        self.assertEqual(ensure_hash_prefix("000"), "#000")
+        self.assertEqual(ensure_hash_prefix("fff"), "#fff")
+        self.assertEqual(ensure_hash_prefix("F00"), "#F00")
+        self.assertEqual(ensure_hash_prefix("123456"), "#123456")
+        self.assertEqual(ensure_hash_prefix("abcdef"), "#abcdef")
+        self.assertEqual(ensure_hash_prefix("ABCDEF"), "#ABCDEF")
+        
+        # Test hex colors that already have #
+        self.assertEqual(ensure_hash_prefix("#000"), "#000")
+        self.assertEqual(ensure_hash_prefix("#123456"), "#123456")
+        
+        # Test invalid inputs (should return unchanged)
+        self.assertEqual(ensure_hash_prefix(""), "")
+        self.assertEqual(ensure_hash_prefix(None), None)
+        self.assertEqual(ensure_hash_prefix("red"), "red")  # Named color
+        self.assertEqual(ensure_hash_prefix("12345"), "12345")  # Wrong length
+        self.assertEqual(ensure_hash_prefix("1234567"), "1234567")  # Wrong length
+        self.assertEqual(ensure_hash_prefix("xyz"), "xyz")  # Invalid hex chars
+        self.assertEqual(ensure_hash_prefix("12345g"), "12345g")  # Invalid hex chars
 
 
 if __name__ == "__main__":