Change colour of object as it passes through a shape

Thanks for reaching out. If you're not doing it repeatedly, manually doing this should be sufficient.

1. Create the text and animate its position using keyframes to make it move from point A to B and pass through the invisible shape. Here's a video that should help you with the position animation: https://adobe.ly/4qLjGYl

2. Apply the Fill effect and animate its colour value at your preferred time. Here's a tutorial that gives a brief introduction to the Fill effect: https://adobe.ly/4ssOizp

If you'd like to do it using expressions, here's a tutorial I found that does something similar: https://adobe.ly/4ssOizp

You man need to make a few changes in the expression in order to achieve what you're looking for.