FiniteStateMachine: add failing doctests: non-hashable colors

The following behaviour is undesired (docstrings says that
colors are tuples of the colors of the constituent states,
but this is not the case and leads to problems in
Automaton.determinisation):

    sage: A = Automaton([[0, 0, 0]], initial_states=[0])
    sage: B = A.product_FiniteStateMachine(A,
    ....:                                  lambda t1, t2: (0, None))
    sage: B.states()[0].color
    [None, None]
    sage: B.determinisation()
    Traceback (most recent call last):
    ...
    TypeError: unhashable type: 'list'

    sage: A = Automaton([[0, 0, 0]], initial_states=[0])
    sage: B = A.composition(A, algorithm='explorative')
    sage: B.states()[0].color
    [None, None]
    sage: B.determinisation()
    Traceback (most recent call last):
    ...
    TypeError: unhashable type: 'list'

Inserted doctests documenting this undesired behaviour.

src/sage/combinat/finite_state_machine.py

@@ -3625,6 +3625,21 @@ def product_FiniteStateMachine(self, other, function,
             ....:                                  only_accessible_components=False)
             sage: H.states()
             [(0, 0), (1, 0), (0, 1), (1, 1)]
+
+        TESTS:
+
+        Check that colors are correctly dealt with. In particular, the
+        new colors have to be hashable such that
+        :meth:`Automaton.determinisation` does not fail::
+
+            sage: A = Automaton([[0, 0, 0]], initial_states=[0])
+            sage: B = A.product_FiniteStateMachine(A,
+            ....:                                  lambda t1, t2: (0, None))
+            sage: B.states()[0].color
+            (None, None)
+            sage: B.determinisation()
+            Automaton with 1 states
+
         """
         result = self.empty_copy()
         if new_input_alphabet is not None:
@@ -3902,6 +3917,17 @@ def _composition_explorative_(self, other):
              Transition from ('B', 1) to ('B', 1): 0|0,
              Transition from ('B', 1) to ('B', 2): 1|0]
 
+        Check that colors are correctly dealt with. In particular, the
+        new colors have to be hashable such that
+        :meth:`Automaton.determinisation` does not fail::
+
+            sage: A = Automaton([[0, 0, 0]], initial_states=[0])
+            sage: B = A.composition(A, algorithm='explorative')
+            sage: B.states()[0].color
+            (None, None)
+            sage: B.determinisation()
+            Automaton with 1 states
+
         TODO:
 
         The explorative algorithm should be re-implemented using the