Remove any unpopped kernels. Mix in candy corn, M&Ms, and nuts.
In a microwave-safe bowl, melt white chocolate on 50% power. Drizzle over the popcorn. Using a spatula, toss the popcorn mixture to coat it with melted chocolate.
Put colored candy melts in two Ziploc bags, microwave candy melts at 50% power for 1 minute. Knead candy in the bag. Continue to microwave and knead at 30-second intervals until smooth and completely melted.
Snip off a small corner of the Ziploc bags and drizzle the melted candy on top of the popcorn.
Let the popcorn rest on the baking sheets until the melted candy is dry, or if you're in a hurry pop it in the fridge to set up.