Hi,
In Runtime, you can create a Graphic with text symbol with a fill background with something like following :
var textGraphic = new Graphic(new MapPoint(0, 2, SpatialReferences.Wgs84));
textGraphic.Symbol = new TextSymbol() { Text = "Simple", Color = Color.Red, Size = 25, BackgroundColor = Color.Yellow };
Above code will add a graphic that looks like image below:
Or you can create a renderer with this symbol and apply renderer to the graphicsOverlay.
But if you are looking at using different background for different text graphics based on some attribute, I am afraid that it is currently not supported.
We do have this feature listed in our future candidates. I will add your use case to our backlog issue and would appreciate if you could you please share your requirement and specific workflow with as much details as possible. An elaborate workflow adds more some weight to the feature and help us prioritize it.
Thanks,
Preeti