flip arguments to Elm function call

Go to the Elm libraries page. Press Standard Libraries. In the search box, type in flip and click the function that comes up. That'll give you the documentation for

flip : (a -> b -> c) -> b -> a -> c
Flip the order of the first two arguments to a function.

With which you can do

flip color (spacer 30 30)

which is the same thing as

\c -> color c (spacer 30 30)