A free program for Android, by ColorFullDay.
Volume Control Style – Custom is an application that allows you to customize the look of the volume control buttons on your device. It’s easy to use and has a lot of options to adjust your phone to your own needs.
You can change the colors, add text, create new themes, change the shape of the buttons, add icons, and so on. It’s a really powerful tool that can give your device a new look.
The only thing you need to do is to install the application and open it. You will be able to customize the volume control style in a few minutes.