double FormatProperties.OpacityDegree of opaqueness (i.e 1.0 -> normal, 0.5 -> 50% transparent). Example = HBox(null, null) { Background: Colors.Gold; Separation: 10; ShowOpacity(each (0.0..1.0 step 0.1));};0%10%20%30%40%50%60%70%80%90%100%