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