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?
Use the Appearance Panel to add a new Fill to your text object by using the “new Fill” icon at the bottom of the panel. Next, highlight this new fill when it appears in the Appearance panel and use the Effect called “Convert to Shape”. You can at this point specify the amount by which you want to grow this fill, in relative or absolute modes. You will see your text covered up by the new fill when you apply the rectangle convert-to-shape effect, so make sure to drag this new fill below the “characters” in the Appearance panel. Now, you have this box which stays in the back of your text, and you can keep adjusting the appearance fill to do further styling as you wish.