diff --git a/homeassistant/components/mqtt/light/schema_basic.py b/homeassistant/components/mqtt/light/schema_basic.py
index 153726a89e8..358a97ed30d 100644
--- a/homeassistant/components/mqtt/light/schema_basic.py
+++ b/homeassistant/components/mqtt/light/schema_basic.py
@@ -495,8 +495,12 @@ class MqttLight(MqttEntity, LightEntity, RestoreEntity):
                 self._attr_color_mode = color_mode
             if self._topic[CONF_BRIGHTNESS_STATE_TOPIC] is None:
                 rgb = convert_color(*color)
-                percent_bright = float(color_util.color_RGB_to_hsv(*rgb)[2]) / 100.0
-                self._attr_brightness = min(round(percent_bright * 255), 255)
+                brightness = max(rgb)
+                self._attr_brightness = brightness
+                # Normalize the color to 100% brightness
+                color = tuple(
+                    min(round(channel / brightness * 255), 255) for channel in color
+                )
             return color
 
         @callback
diff --git a/tests/components/mqtt/test_light.py b/tests/components/mqtt/test_light.py
index 1e486a3492c..fcdec1fbfe3 100644
--- a/tests/components/mqtt/test_light.py
+++ b/tests/components/mqtt/test_light.py
@@ -636,8 +636,8 @@ async def test_brightness_from_rgb_controlling_scale(
             }
         },
     )
+    mqtt_mock = await mqtt_mock_entry_with_yaml_config()
     await hass.async_block_till_done()
-    await mqtt_mock_entry_with_yaml_config()
 
     state = hass.states.get("light.test")
     assert state.state == STATE_UNKNOWN
@@ -650,10 +650,29 @@ async def test_brightness_from_rgb_controlling_scale(
     state = hass.states.get("light.test")
     assert state.attributes.get("brightness") == 255
 
-    async_fire_mqtt_message(hass, "test_scale_rgb/rgb/status", "127,0,0")
+    async_fire_mqtt_message(hass, "test_scale_rgb/rgb/status", "128,64,32")
 
     state = hass.states.get("light.test")
-    assert state.attributes.get("brightness") == 127
+    assert state.attributes.get("brightness") == 128
+    assert state.attributes.get("rgb_color") == (255, 128, 64)
+
+    mqtt_mock.async_publish.reset_mock()
+    await common.async_turn_on(hass, "light.test", brightness=191)
+    await hass.async_block_till_done()
+
+    mqtt_mock.async_publish.assert_has_calls(
+        [
+            call("test_scale_rgb/set", "on", 0, False),
+            call("test_scale_rgb/rgb/set", "191,95,47", 0, False),
+        ],
+        any_order=True,
+    )
+    async_fire_mqtt_message(hass, "test_scale_rgb/rgb/status", "191,95,47")
+    await hass.async_block_till_done()
+
+    state = hass.states.get("light.test")
+    assert state.attributes.get("brightness") == 191
+    assert state.attributes.get("rgb_color") == (255, 127, 63)
 
 
 async def test_controlling_state_via_topic_with_templates(