Pulseaudio/backlight slider add icons or something that indicates which is which 

I have currently enabled pulseaudio/slider and backlight/slider and they look identical.

 I would like to add some icons to the left of the bars to indicate which is for volume and which is for brightness.

 How can I do this? I could change the background color of the bars but I would really like to add some icons to the left of each bar to display volume/brightness. 