transparency between two qwtPlot

hi friends/Experts,
I have added two qwtPlot on a same window. user can move the plot on the parent widget area.
how i can set transparency between the qwtplot when one plot is top on the other plot so that both plot curves can be visible if it aligns one top of other.

please help me.

Well - there is not much difference to any other type of widgets. Use transparent alpha values for the colors.

Uwe