I had a fading plastic pumpkin and on a whim I sprayed it with orange metalcast spray paint and was impressed with the outcome. It's kind of transparent and I purchased it to color light bulbs. https://www.duplicolor.com/products/metalCast/
Nice movement and sound. I'm assuming that he's being electrocuted through his wrist as most electric chairs have a skull cap with wires attached. That would finish off your prop. Please provide a tutorial for your pneumatics as this is a great prop.