I've wanted to try this now for a while, and a few weeks ago I finally bought a piece of red film, which is necessary to implement the idea. I actually wanted to buy an orange sheet, but I only found red.
The basic idea is to attach a piece of colored film, cut to shape for the Diana, specifically for the window the film is later placed over.
Since the colored film “eats away” quite a lot of light, this must be compensated for with the camera settings. In very sunny weather, I use the normal Diana lens and have the aperture set to cloudy. In the shade the wide-angle and super wide-angle lenses were used, the aperture setting was still on cloudy. As you can see from the photos, most of the contrast is lost through the red sheet, but I still like several of the pictures very much anyway. If I should ever find an orange sheet, I will definitely try it out again.