Change background color with ng-Style
You can't do ternary conditions within a tag and you have an error since you didn't quote background-color. You have to either quote it, or use camelCase, while the conditions should be set in the controller.
So, the fix is to have a scope variable denoting a color (or the full style object) and use it like this: http://plnkr.co/edit/iYkSa2I1ysZutdkAKkuh?p=preview
Here's an example you could use to make your code work with your DB (I'm calling external JSON here, but the principle is the same): http://plnkr.co/edit/Kegs95NNyGGySMDzhQed?p=preview
This way you could fetch the 'selected' color as well. That's pretty much all I can tell you with the info you provided.