A way to combine FillBetween and Legend?

[aeroflux]

I am currently plotting six curves to a plot whilst using draw_grid for both x and y. What I would like to have is a white background behind the legend as the grid lines interfere with the text.

One idea i thought I would try is using FillBetween. But when I use "add(p, FillBetween(x1, y1, x2, y2))" and providing coordinates i.e. .1,.9,.2,.7 I only get a "Error: 'reverse' has no mention..."

Many thanks.