It is not only a usablity problem, but rather a performace issue.

Compile and run the following example.
Click somewhere inside and you'll see
that right side color flicks unexpectedly.

========== SOURCE ==========
import javafx.animation.Timeline;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.paint.Color;
import javafx.scene.shape.Rectangle;
import javafx.stage.Stage;
import javafx.util.Math.random;

var timer: Timeline on replace old {
  old.stop();
  timer.playFromStart();
}

var c1 = Color.BLUE;
var c2 = Color.BLUE;

def w: Number = bind stage.scene.width / 2;
def h: Number = bind stage.scene.height;

def stage: Stage = Stage {
  title: "JavaFX test"
  scene: Scene {
    width: 640
    height: 480
    content: Group {
      onMouseClicked: function (event) {
        def color = Color.color(random(), random(), random());
        timer = Timeline {
          keyFrames: at (1s) {
            c1 => color;
            c2 => Color.color(random(), random(), random());
          }
        }
      }
      content: [
        Rectangle { width: bind w height: bind h fill: bind c1 }
        Rectangle { width: bind w height: bind h fill: bind c2 x: bind w }
      ]
    }
  }
}