Hey just to let you know, I know it’s 5 months old, but in case someone new to WordPress is wondering how to edit this feature, you can do so by adding this after the song
|bgcolor=#HEX
For example:
[audio https://www.yourwordpressblog.com/wp-content/uploads/2014/06/Awesome-Song.mp3|bgcolor=#FFFFFF]
You can also add other features or customize certain parts of the player like the text or the color of the tracker etc by adding the same thing: For example:
[audio https://www.yourwordpressblog.com/wp-content/uploads/2014/06/Awesome-Song.mp3|bgcolor=#FFFFFF|titles=My Song|remaining=yes|loop=yes|animation=no|tracker=0x99ccff|text=0xFFFFFF]
|titles displays whatever you want the title to appear as when play is clicked
|remianing displays the remaining total of song
|loop enables loop
|animation leaves the player open
|tracker changes the color of the tracker
|text changes the color of the text displayed
etc etc etc there are many more advanced options