[igraph] problem saving to postscript file-- edges don't show up

[Susan Biancani]

I'm trying to save a plot of a graph as a postscript file, but when I open the file in Adobe Illustrator, it has no edges. I get a warning when I execute my code. Here are the code and the warning:

V(g.art)$color <- rgb(red = .35, blue = .35, green = .35, alpha=.8) #gray
V(g.art)[V(g.art)$clust == 0]$color <- rgb(red = 1, blue = .25, green = .25, alpha=1) #red
V(g.art)[V(g.art)$clust == 6]$color <- rgb(red = .45, blue = 1, green = .45, alpha=1) #blue
V(g.art)[V(g.art)$clust == 7]$color <- rgb(red = .2, blue = .15, green = .6, alpha=1) #green
V(g.art)[V(g.art)$category == 1]$shape <- "circle"
V(g.art)[V(g.art)$category == 2]$shape <- "square"
E(g.art)$color <- rgb(red=0, green=0, blue=0, alpha=0.1)
postscript("all_clusters.eps", fonts=c("serif", "Palatino"))
plot(g.art, layout=layout.fruchterman.reingold, edge.arrow.size=0, vertex.label.family="serif", edge.label.family="Palatino", vertex.label.color = "black", vertex.label.cex = 0.7, vertex.size = 8)

Warning message:
In segments(x1, y1, x2 + r.seg * cos(th.seg)/uin[1], y2 + r.seg *  :
  semi-transparency is not supported on this device: reported only once per page

dev.off()

When I open the postscript file, the nodes and labels are there, but no edges.

Only the edges were semi-transparent, so I tried setting alpha=1 for the edges, but I get the same results. Has anyone dealt with something like this before?

Thanks,
Susan