Thank you both! Right now, we are using Instamorph for the horns. Our theory is if we make it thin enough, the light should successfully come through. My only worry is about the green horns turning red. I'm hoping buying a bright enough light should be okay.
Do the lights animate and dance around, or would you be okay with simple illuminated horns?
The horns just light up. No fancy color changes or flashes, so I'm guessing the LED's will be just fine. I'll post again with the final result so I can share what works and what doesn't!