[Line] Dissociate line color and area color

[LeopoldArkham]

In a line graph, I can't seem to find a way to dissociate the color of the line from the color of the area, i.e. be able to pass two different colors to a line and its area respectively.

I suppose I could disable areas in Nivo, and recompute each of them( this is a stacked line graph) with their own color as layers, but that wouldn't be worth it in my use case for a cosmetic change.

Is there a built-in way to accomplish this that I missed?

Otherwise, if the maintainers can give me with an API they'd be okay with (and how it would interact with areaOpacity), I would be up for implementing this; looking at the internals it doesn't seem too hard to do.