diff --git a/docs/design/type-notation.typ b/docs/design/type-notation.typ
index 18e7d95..7858b50 100644
--- a/docs/design/type-notation.typ
+++ b/docs/design/type-notation.typ
@@ -9,6 +9,11 @@ Operator signature that takes two unnamed arbitrary numbers of the same type and
 Op<T: Num> [ T T ] -> T
 ```
 
+Operator signature that takes any color and any number type, and returns a color again:
+```iowo
+Op<C: Color, M: Num> [ C M ] -> C
+```
+
 Operator that takes a 32 bit signed integer and returns another:
 
 ```iowo