Just use an animated image and put it in your clipboard. Then use the
clipboard image to create the text!
Here is an example of what I made in 5 easy steps!
Here's how I did it in 5 steps
1. Opened a static Rainbow graphic. (you'll have to find your own graphic)
2. Selected Animation -> Anim Roll -> Left to Right to create the animated background
3. Selected Edit -> Copy image to clipboard
4. then I started a new image. File -> New Blank Image
5. Selected Draw -> Text Tool. I wrote MyTheme in the text and selected
Pattern: "Your Clipboard"
And that's it.