Question: view, display and plot question?

I have been able implement this procedure here. 

AreaBetween := overload([proc(fnc::{list}, a::anything, b::anything, col::list) option overload; plottools:-transform(unapply([x, y + fnc[2]], x, y))(plot([fnc[1]] + [-fnc[2]], x = a .. b, col = [col[2], col[3]], gridlines, size = [600, 600], thickness = 3, filled = [color = col[1]])); end proc])

1) How do get to construct a larger canvas? Meaning if I want a xy axis, x = -10..10, y = -10..10 however only x = a..b is suppose to be shaded. Can I do that with my procedure? 

2) Only the lower graph is colored currently. How do I get it to color the upper graph? 

Many thanks in advance. 

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