How to change app text color or background color in Android Studio Panda 3?

I have installed Android Studio Panda 3 and have created a default ‘Empty Activity’ project.

When I connect a physical tablet, I can see the text that this app creates (“Hello Android!”).

The problem that I am having is that when I add a virtual device, I cannot see the text. It’s possible that this is because the virtual device has a black background and the text is also black. My tablet has a white background with its black text.

How do I change either the text color or the background color for this app? Can this be done in the main .kt file or do I have to modify one of the .xml files?