doc/signaltypes: add hue placeholder

We will have to add a helpful diagram, but having the placeholder allows us to link to it already.

doc/api/signaltypes.rst

@@ -242,3 +242,11 @@ Fahrenheit (°F) or Kelvin (K), you can use the following conversion formulas:
     :math:`°\!F = °\!C \cdot \frac{9}{5} + 32`.
 
     :math:`K = °\!C + 273.15`.
+
+.. _hue:
+
+hue: deg
+--------------
+Hue of a color (0-359 degrees).
+
+TODO: diagram

pybricks/_common.py

@@ -448,7 +448,7 @@ class ColorLight:
         """Set the hue, saturation and brightness of the light.
 
         Arguments:
-            hue (:ref:`angle`): Hue of the color.
+            hue (:ref:`hue`): Hue of the color.
             saturation (:ref:`percentage`): Saturation of the color.
             value (:ref:`percentage`): Brightness value of the color.
         """

pybricks/pupdevices.py

@@ -212,7 +212,7 @@ class ColorSensor:
 
         :returns: Tuple with the hue, saturation, and value
             (brightness) of the color.
-        :rtype: (:ref:`angle`, :ref:`percentage`, :ref:`percentage`)
+        :rtype: (:ref:`hue`, :ref:`percentage`, :ref:`percentage`)
 
         """
         pass