Very strange behaviour...

I've noticed that something is changing the background colour of my app after a period of inactivity. This is occurring on a Roku Express with the screensaver disabled and the theme set to "Nebula". After launching the app, if i leave it for around an hour, the background colour has been changed from white (#EFEFEF) to black? I've added code to observe the field and can confirm that it is being changed but there is nothing in my app doing this. Has anyone ever came across this before?