Allow to set background color for each app button, fix couple comments in sample config

config.go

@@ -120,6 +120,7 @@ type MyConfig struct {
 		Instance            string   `json:"instance,omitempty"`
 		Class               string   `json:"class,omitempty"`
 		Color               string   `json:"color,omitempty"`
+		Background          string   `json:"background,omitempty"`
 		Border              string   `json:"border,omitempty"`
 		BorderActive        string   `json:"border_active,omitempty"`
 		Separator           bool     `json:"separator,omitempty"`
@@ -383,6 +384,10 @@ func readConf() (MyConfig, error) {
 				app.Color = Conf.Color
 			}
 
+			if app.Background == "" {
+				app.Background = Conf.Background
+			}
+
 			if app.Border == "" {
 				app.Border = Conf.Color
 			}

i3status-go-example.json

@@ -1,6 +1,8 @@
 {
-// Default text and *block* background colors
+// Default text and *block* border colors. If not set #3e78fd is used.
 "color" : "#3e78fd",
+
+// Default backbround color. If not set value of #edeceb is used.
 "background" : "#000000",
 
 // Load Average
@@ -156,6 +158,8 @@
 			"class": "^Thunar$",
 			// text color in html notation
 			"color": "#ffa500",
+		    // background color in html notation
+		    "background" : "#000000",
 			// border color in html notation
 			"border": "#666666",
 			// border color if there is at least one window with given Instance and/or Class exist

main.go

@@ -136,7 +136,7 @@ func main() {
 					var b I3BarOutBlock
 
 					b.FullText = app.FullText
-					b.Background = Conf.Background
+					b.Background = app.Background
 					b.Color = app.Color
 					b.Instance = app.Instance
 					b.Markup = `pango`