ScrollPanes in JavaFX 8 always have gray background

I found the solution in this discussion: https://community.oracle.com/thread/3538169

First I needed this:

.scroll-pane > .viewport {
   -fx-background-color: transparent;
}

Then I could set the background color to whatever I like. In this case, I’m making all ScrollPane backgrounds transparent:

.scroll-pane {
   -fx-background-color: transparent;
}