Fix color less than or equal to

tutor/database.py

@@ -1,5 +1,6 @@
 import datetime
 import decimal
+import itertools
 import logging
 import typing
 import uuid
@@ -123,7 +124,14 @@ async def advanced_search(
                 constraints.append(f"cards.color_identity ILIKE %({param})s")
                 params[param] = tutor.models.Color.to_string(criterion.colors)
             if criterion.operator == tutor.search.Operator.lte:
-                colors = list({str(color) for color in criterion.colors} | {""})
+                colors = list(
+                    {
+                        tutor.models.Color.to_string(list(combo))
+                        for n in range(len(criterion.colors))
+                        for combo in itertools.combinations(criterion.colors, n + 1)
+                    }
+                    | {""}
+                )
                 constraints.append(
                     "({})".format(
                         " OR ".join(