An advice for a specific kind of RRDtool graph

I'm trying to graph some data with RRDtool and I have problems with defining the exact graph command.

The kind of graph I want is something like this: http://oss.oetiker.ch/rrdtool/gallery/gate.spamd.week.600.png - th开发者_Go百科e blue graph.

I can not "cook up" the definition for creating a graph like the one which is light blue and is on the background. It's a something between a line and an area :) . Any ideas what can I try?

Thank you in advance!

I guess it is an area stacked on a transparent area or on a line ... in that way you can create a 'floating' area.