plotter: BarChart draws semi-transparent colors grey

[gaboose]

What are you trying to do?

Set a semi-transparent color to a barchart.

What did you do?

func main() {
	p, _ := plot.New()
	rand.Seed(int64(0))
	v := make(plotter.Values, 20)
	for i := range v {
		v[i] = float64(rand.Intn(20))
	}
	barChart, _ := plotter.NewBarChart(v, 8)
	barChart.Color = color.RGBA{R: 255, G: 255, B: 0, A: 128}
	p.Add(barChart)
	p.Save(4*vg.Inch, 4*vg.Inch, "out.png")
}

What did you expect to happen?

Yellow bars like this to be produced, only a little less bright:

What actually happened?

Grey bars:

What version of Go and Gonum/plot are you using?

go version go1.12.2 linux/amd64
$ echo (cd (go env GOPATH)/src/gonum.org/v1/plot; and git rev-parse HEAD)
3a5f52653745fa15b552c97e1d8052e496e85503

Does this issue reproduce with the current master?

3a5f52653745fa15b552c97e1d8052e496e85503 is master

[sbinet]

try with:

--- ./main.go.old	2019-04-30 09:50:12.042685394 +0200
+++ ./main.go.new	2019-04-30 09:49:52.872685744 +0200
@@ -17,7 +17,7 @@
 		v[i] = float64(rand.Intn(20))
 	}
 	barChart, _ := plotter.NewBarChart(v, 8)
-	barChart.Color = color.RGBA{R: 255, G: 255, B: 0, A: 128}
+	barChart.Color = color.NRGBA{R: 255, G: 255, B: 0, A: 128}
 	p.Add(barChart)
 	p.Save(4*vg.Inch, 4*vg.Inch, "out.png")
 }

[gaboose]

that works! thanks!