It is possible to have an overlay applied to your screen when you put a pumpkin on your head.
But can you have more than one of these custom overlays? Perhaps by using a texture pack or maybe changing the overlay based on the name of the pumpkin?
I'd like to have different colour blur effects based on the colour of the Pumpkin, eg If the pumpkin's name is '1', show a green blur effect. If it is '2' show a blue blur effect, and so on.