I think the belt color should not be only on the top of the belt where it can easily be almost completely blocked by whatever is on the belt.
Maybe something like this could work? (mspaint illustration)
![Image](https://forums.factorio.com/images/ext/e9d1ee7efadbc5e64c9583e311268cb1.png)
Another possibility is maybe the whole metal bottom part could be slightly colored?