Gadfly: transparent histogram layers

Specific Domains Visualization
5

This is just a comment. It would be nice in Gadfly if one could use transparent colors with the color aesthetic. The following example would benefit if transparent colors could be used:

D1 = vcat([DataFrame(x=i+randn(200), g="μ=$i") for i in [0,2] ]...)  

coord = Coord.cartesian(xmin=-6, xmax=6)
p = plot(D1, x=:x, color=:g, coord,
    Stat.density(bandwidth=0.5), 
    Geom.polygon(fill=true, preserve_order=true),
)

fig3