Gadfly: How to change width and opacity of lines in Geom.density?

Specific Domains Visualization
, , ,
4

Theme(alphas= ) is the alpha palette for the alpha aesthetic and Scale.alpha_discrete (see Gadfly Tutorial). alpha and color are separate aesthetics, which is why a is ignored in color=[RGBA(r,g,b,a)].
Currently, the alpha aesthetic been enabled for Geom.point, Geom.polygon, and Geom.ribbon, but not Geom.line.

There is also Theme(lowlight_color= ), which is old pre-alpha code. This was enabled for Geom.polygon and Geom.ribbon and controls stroke color (fill=false) or fill color (fill=true). It must be a function, e.g.

using Colors
gp = Geom.polygon(preserve_order=true)
p = plot(x=rand(20), Stat.density, gp,
#    Theme(lowlight_color=x->"gray", line_width=3pt)
    Theme(lowlight_color=x->RGBA(x,0.3), line_width=3pt)
)

More examples of Stat.density and Scale.alpha_.