I have done it really cheaply, with red self adhesive book covering, which is probably not UV stable or anything useful like that, but it looks pretty nice for $2.50... Can always remove it if it starts to fade (hope so anyway, I waxed the lenses thoroughly before application).
First light done... The contact was cut roughly to size, stuck on and smoothed out to eliminate wrinkles. Then I cut carefully around the groove at the edge of the orange lens.
Both lights completed. The light output is red-orange (not to be unexpected I guess)
