[NTG-context] Changing the colors of a button

I am trying the following: \button[backgroundcolor=darkgray,framecolor=black,framecorner=round]{Go Back}[PreviousJump] The parameter framecolor works (I tried it with green). Framecorner works also, but backgroundcolor not. How can I change the background and text color of the button? Also would it not be better when clicking on this button, the highlighting also works with rounded corners? -- Cecil Westerhof