ggplotd - curve colour

[brocolis via Digitalmars-d-learn]

Is this correct usage?
auto gg = GGPlotD().put( geomLine( Aes!(typeof(xs), "x", 
typeof(ysfit), "y", string, "colour")( xs, ysfit, "red") ) );

The output is a blank png file.

Full source:
import ggplotd.ggplotd;
import ggplotd.geom;
import ggplotd.aes;
import ggplotd.axes;

void main()
{
     import std.array : array;
     import std.algorithm : map;
     import std.range : iota;
     import ggplotd.colour;

     auto f = (double x) { return x; };
     auto xs = iota(-5, 5, 0.1 ).array;
     auto ysfit = xs.map!((x) => f(x)).array;
     auto gg = GGPlotD().put( geomLine( Aes!(typeof(xs), "x", 
typeof(ysfit), "y", string, "colour")( xs, ysfit, "red") ) );

     gg.put( xaxisOffset( 0) ).put( yaxisOffset( 0) );
     gg.save( "axes.png", 500, 300 );
}