Makie isosurface transparency?

Ok, getting closer. Still puzzling: I make a torus geometry. Why isn’t the full torus visible even though there is an alpha? It seems that the alpha is applied to another surface (dual ellipsoid case above), but not to different parts of the same surface. We should be able to see the core of the torus, and the back surface:

using GLMakie
using ColorSchemes
cmap3 = get(colorschemes[:plasma], LinRange(0,1,100))
	cmap4 = [(cmap3[i],0.65) for i in 1:100]
	ξ = -40:1:40
	c = 20
	a = 15
	torus = [((hypot(X,Y)-c)^2+Z^2-a^2) for X in ξ, Y in ξ, Z in ξ]
	volume(torus, algorithm = :iso,isovalue =100,isorange =50, colormap=cmap4)
	current_figure()

I would expect something more like this:

Screen Shot 2021-08-20 at 2.02.55 PM