Here is an example that hopefully will get you started.
The example shows that you can press a button on a parent form and this will raise an event on all children in a repeating panel.
Now, of course you will need to extent this example, but in general, from what I can understand, the concept is the same. In your case you would have a text box somewhere, and its change event would raise events on all children panels, changing background color where needed.
I hope this helps point you in the right direction.
I should also mention that you can also loop through repeating panel components with self.repeating_panel_1.get_components()
. This would allow you to set up some logic as you iterate through each child.