Go to a place that rents DJ equipment or concert equipment and buy a red gel. Then cut to size.
These are used on lights to change the colours of lighting. I use red gels on all my games with orange display. Cheap as chips, too.
Just saw you are in Ottawa, there is a place in Bells Corners that sells the gels. That's where I got mine. The name of the place is Fleet Pro Sound and Lighting.