I have found a number of solutions to adding color to a text box in earlier versions of Illustrator, but they don't seem to work in the current version.
When I use the Direct Selection tool to select the text box, it activates the "path" in the appearance panel and allows me to set a stroke and fill for that path, but the stroke and fill aren't actually applied to the selected text box.
In this picture you can see that I have selected the text box, and my appearance panel gives me the options to set the stroke and fill for the path (and it looks like Type is in a layer above the path)
For now, I will use the clunky option of grouping my text box with a filled rectangle below it, but it seems that earlier versions of Illustrator allowed the better option (like you can do in InDesign). Did they really remove it in this version?