See https://community.oracle.com/thread/3556709

WARNING: Could not resolve '-fx-color' while resolving lookups for '-fx-background-color' from rule '*.menu-down-arrow' in stylesheet jar:file:/C:/Program%20Files%20(x86)/Java/jdk1.8.0_05/jre/lib/ext/jfxrt.jar!/com/sun/javafx/scene/control/skin/caspian/caspian.bss

This warning also happens with other properties and other CSS selectors ("rule"), but for now I've only saw it for "color-related" properties.

Unfortunately I didn't find an isolated small test case which I could attach, but this error occurs randomly but often enough in our application.

I am not sure, but it *might* be related to Popups and Stages, i.e. when you open a Popup or Stage this warning comes. I also saw that e.g. a MenuItem in a ContextMenu did not have a background-color, which might be caused by this warning.

Further information, which might be helpful:
We use Caspian style and we added a custom stylesheet to each Scene, the root looks like this:

.root {

    -fx-base: #ececec;
    -fx-color-transparent: rgba(255, 255, 255, 0.55);
    -fx-background: #f8f8f8;

    -fx-accent: #0074bc;
    -fx-focus-color: #0074bc;

    -fx-color: -fx-base;
    -fx-mark-color: ladder(-fx-color, white 10%, derive(-fx-color, -63%) 11%);
    -fx-selection-bar: linear-gradient(to top, derive(-fx-background, -2%) 0%, derive(-fx-background, 50%) 100%);
    -fx-cell-hover-color: linear-gradient(to top, #99c7e4 0%, #e5f1f8 100%);
}


If I can come up with a test case, I will post it here. But maybe somebody already has an idea.