Overlays are GPU-accelerated pixel layers added on top of the visual. There are up to 4 layers available.
For each layer you can pick one of:
A solid color is an HSV color. Like colors in the parameter section, it can be picked from the currently chosen palette in the same way.
Image is a PNG file with optional alpha loaded from disk.
To add your own images, put them in the "overlays" directory. The player reads them when starting up so you might have to restart the player.
If you are on a multi PC setup, bear in mind that the images must be put into the same machine as the player manager and consequently, player.
You can choose an alpha (transparency) value with a slider.
You can choose from most of the common blend modes: