Hey,
you were right. The Color is correct but the Brightness not. But this is only with the Colorpicker. When i use:
sendCommand(new HSBType(new DecimalType(18), new PercentType(87), new PercentType(37)))
it works perfectly!
But there is also an Error in the Feedback from the Controller.
For Example you choose Red as Color the Controller changed to Red (with 100% Brightness) but the Feedback is an completely other Color, so the Colorpicker jumps around.
I will post this as desired @ Github