The following CSS style used to work in javafx 1.3:

    -fx-hover-base: ladder base stops
        (20%,derive(-fx-base,20%))
        (35%,derive(-fx-base,30%))
        (50%,derive(-fx-base,40%));

In javafx 2.0 I get the following exception when I hover a button using that style:

WARNING: com.sun.javafx.css.StyleHelper lookup caught:
java.lang.ClassCastException: java.lang.String cannot be cast to javafx.scene.paint.Color
at com.sun.javafx.css.parser.LadderConverter.convert(LadderConverter.java:27)
at com.sun.javafx.css.parser.LadderConverter.convert(LadderConverter.java:9)
at com.sun.javafx.css.Value.convert(Value.java:143)
at com.sun.javafx.css.parser.DeriveColorConverter.convert(DeriveColorConverter.java:30)
at com.sun.javafx.css.parser.DeriveColorConverter.convert(DeriveColorConverter.java:12)
at com.sun.javafx.css.Value.convert(Value.java:143)
at com.sun.javafx.css.parser.StopConverter.convert(StopConverter.java:32)
at com.sun.javafx.css.parser.StopConverter.convert(StopConverter.java:13)
at com.sun.javafx.css.Value.convert(Value.java:143)
at com.sun.javafx.css.converters.PaintConverter$LinearGradientConverter.convert(PaintConverter.java:102)
at com.sun.javafx.css.converters.PaintConverter$LinearGradientConverter.convert(PaintConverter.java:80)
at com.sun.javafx.css.Value.convert(Value.java:143)
at com.sun.javafx.css.converters.PaintConverter$SequenceConverter.convert(PaintConverter.java:68)
at com.sun.javafx.css.converters.PaintConverter$SequenceConverter.convert(PaintConverter.java:53)
at com.sun.javafx.css.Value.convert(Value.java:143)
at com.sun.javafx.css.StyleHelper.lookup(StyleHelper.java:489)
at com.sun.javafx.css.StyleHelper.lookup(StyleHelper.java:429)
at com.sun.javafx.css.StyleHelper.transitionToState(StyleHelper.java:266)
at javafx.scene.Node.impl_processCSS(Node.java:5375)
at javafx.scene.Parent.impl_processCSS(Parent.java:943)
at javafx.scene.Parent.impl_processCSS(Parent.java:950)
at javafx.scene.control.Control.impl_processCSS(Control.java:783)
at javafx.scene.Scene.doCSSPass(Scene.java:409)
at javafx.scene.Scene.access$2500(Scene.java:118)
at javafx.scene.Scene$ScenePulseListener.pulse(Scene.java:1576)
at com.sun.javafx.tk.Toolkit.firePulse(Toolkit.java:264)
at com.sun.javafx.tk.quantum.QuantumToolkit.pulse(QuantumToolkit.java:355)
at com.sun.javafx.tk.quantum.QuantumToolkit$10.run(QuantumToolkit.java:291)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.access$100(WinApplication.java:29)
at com.sun.glass.ui.win.WinApplication$1$1.run(WinApplication.java:49)
at java.lang.Thread.run(Thread.java:619)