Originally designed to tint page sections, they will also work on many other things.
These are like colored transparent cellophane, so whatever is directly below will show through. 
Won't work at same level as the background images, they need to be on a level above them.
It's one reason my templates have duplicated nested sections.

Will work in many other areas.
One example: images on our templates have default frames, if applied to images these will tint those frames.