.., a quick way of exploring blend-modes if you cant remember their names
(define blend-modes
#("zero" "one" "dst-color" "one-minus-dst-color"
"src-alpha" "one-minus-src-alpha" "dst-alpha"
"one-minus-dst-alpha" "src-alpha-saturate"))
(define (blend src dest)
(blend-mode
(vector-ref blend-modes src)
(vector-ref blend-modes dest)))
then a function like (blend 3 1) should work