Selectable theme colour

[freshollie]

To quote @Jesey158 from #3

I got the link from Walter Zengel, because I have used the app of him so far.
Have now your current app on my Nexus 7 (2013) with Timurt's kernel installed. Works so far quite well. The tablet is installed in the Audi and connected with a Joycon.exc to the Can bus. So I can control the tablet via the steering wheel remote control. Your app also reacts very well to select the stations with the next track previus track.
But when I press the back button closes the app, but the audio output continues unfortunately. Is it possible to use the exit button with a hardware key?
And the app is blue as a background. How could I change the red (because in the Audi)

I have created a new issue for this problem as it does not relate to #3.

To summarise, the radio player will act like any other media player. The pause button can be used to pause it or the enter key while in the app.

I will look into theming