Gah - a solution with more questions. – EntropicLqd

From Unreal Wiki, The Unreal Engine Documentation Site

Draws a material onto the entire screen.

See CameraEffect for instructions on how to use the camera overlay and other camera effects correctly.

[edit] Properties

color OverlayColor 

Color of the material to draw. Use white (R, B, G and A set to 255) to draw it in its original colors. This works exactly like the Canvas DrawColor.

Material OverlayMaterial 

The material to overlay.