ADDITIONAL SYSTEM INFORMATION :
C:\Users\hwaite>ver

Microsoft Windows [Version 10.0.17134.228]

C:\Users\hwaite>"%JAVA_HOME%\bin"\java -version
java version "1.8.0_181"
Java(TM) SE Runtime Environment (build 1.8.0_181-b13)
Java HotSpot(TM) 64-Bit Server VM (build 25.181-b13, mixed mode)

A DESCRIPTION OF THE PROBLEM :
'Mnemonic' underline should adopt same color as the text it's underlining. This is not happening when the latter's foreground color is modified by style.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Launch program and press 'Alt' key.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Mnemonic underline is white.
ACTUAL -
Mnemonic underline is black.

---------- BEGIN SOURCE ----------
public class Test extends Application {
    @Override
    public void start(Stage pStage) {
        final Button btn = new Button("_Foobar");
        btn.setStyle("-fx-background-color: #c4052f; -fx-text-fill: #ffffff");
        pStage.setScene(new Scene(new StackPane(btn), 300, 250));
        pStage.show();
    }

    public static void main(String[] pArgs) {launch(pArgs);}
}
---------- END SOURCE ----------

FREQUENCY : always