Take a red, green, and blue gel and make three images of a single subject. Combine everything in Photoshop and set the images to the Screen overlay mode. Adjust curves and color balance to create a full color image.
This is a great way to educate folks in a digital photography class on the additive and subtractive color spectrum. I’ve been teaching it for years and the results from students are always unique and interesting, their happy accidents always lead to interesting imagery.