How to add an overlay to camera view

I would like to add an overlay to the camera view..ideally a filter overlay - how can I accomplish this?

[GabrielAlva]

Hi,
You can add a sub view to the camera view with the filter.

Adding a sub view to the camera view is not displaying. Furthermore, I have tired adding a sub view to the super view of the camera view and then bringing camera view to the front but I still do not see the sub view..