[NTG-context] My own backgroundcolor in a frame

Dear List! I have the following example: \defineframedtext [prettyblock] [width=10cm, indenting={yes, small}, background=color, backgroundcolor=lightgreen, foreground=color, foregroundcolor=black , offset=2mm, align=flushleft] My problem is now: how can I write, if I have an Rgb Color and I do not know the name. I have looked at the list, but cannot find the color. Can I say: background=color, backgroundcolor=rgb and put the numbers in (lets say: r=200, g=112, b=300)? Is that correct, or do I have to take a special way? Or do I have to define it? Many thanks and regards Uschi Hermann