[Pharo-project] How to set the color of a gradient button ?

On button created with polymorph, like btn := self newButtonFor: self action: #openFinish label: 'J''ai fini !' help: 'Presse ce bouton lorsque tu as fini l''exercice'. ^ btn onColor: Color green muchLighter offColor: Color gray Changing the color does not work as expected. There are a couple of metod to change the color but none are working. Hilaire -- http://blog.ofset.org/hilaire