I have been developing a Tkinter application that has a label in it. This label needs to be set to a certain color when a variable equals something, and something else when it equals something else. However, I can't see how to make this logic execute throughout the whole lifespan of the application. 

Here is what I have so far:

```
if variableName.get() == "":
    label4.config(bg = "SystemButtonFace")
else:
    label4.config(bg = "lawngreen")

```

Thanks in advance!