cmd,example: fix uses of color.NRGBA

Signed-off-by: Egon Elbre <egonelbre@gmail.com>

example/hello/hello.go

@@ -41,7 +41,7 @@ func loop(w *app.Window) error {
 		case system.FrameEvent:
 			gtx := layout.NewContext(&ops, e)
 			l := material.H1(th, "Hello, Gio")
-			maroon := color.RGBA{127, 0, 0, 255}
+			maroon := color.NRGBA{R: 127, G: 0, B: 0, A: 255}
 			l.Color = maroon
 			l.Alignment = text.Middle
 			l.Layout(gtx)