Cover each of 3 large baking sheets with parchment paper. Set aside. Set out 3 large bowls and set aside until popcorn is popped.
Heat 3 tablespoons coconut oil in large pot over medium heat, being very careful not to burn oil. When oil is hot and shimmering, add 2 to 3 kernels to test oil. When test kernels pop, add remaining ½ cup popcorn kernels and immediately cover pot with lid. Secure lid with one hand and shake pot until kernels begin to pop. Once kernels begin to pop rapidly, return pot to heat.
Listen closely to popping kernels and shake pot periodically. When popping slows to approximately 3 to 5 seconds between pops, remove pot from heat. If desired, sprinkle popcorn salt over popcorn in pot and toss to coat, then divide popcorn evenly among 3 large bowls. Remove any unpopped kernels.
Place 2 cups white chocolate and 1 teaspoon coconut oil in each of 3 microwave-safe mixing bowls.
Place one bowl of white chocolate in microwave. Microwave 30 seconds, then stir with dry spatula. Repeat, microwaving in 30 second intervals and stirring after each, until white chocolate is completely melted. Note: Be careful not to burn chocolate. If chocolate seizes, stir in coconut oil in ¼ teaspoon increments until mixture is smooth.
When chocolate is melted, carefully remove bowl from microwave. Add 2 to 3 drops orange (or red and yellow) food coloring to bowl and stir until color is fully incorporated. Add more food coloring as needed, mixing well after each addition, until desired shade is achieved.
Transfer orange-colored white chocolate to one large mixing bowl with popcorn. Gently toss or stir until popcorn is fully coated in white chocolate.
Transfer coated popcorn to one baking sheet lined with parchment paper. Gently spread popcorn out into one flat, even layer. While chocolate is still melty, sprinkle one third of desired mix-ins over top of popcorn. Set baking sheet with prepared orange popcorn aside.
Repeat steps 5 through 8 with second bowl of white chocolate, green (or yellow and blue) food coloring, popcorn, and desired mix-ins. Set baking sheet with prepared green popcorn aside.
Repeat steps 5 through 8 with second bowl of white chocolate, purple (or red and blue) food coloring, popcorn, and desired mix-ins. Set baking sheet with prepared purple popcorn aside.
Leave all three colors of prepared popcorn to dry 5 minutes. Once chocolate is completely dry, break each color of popcorn into pieces, chunks, or clusters. Transfer popcorn to large bowl or cauldron to serve. Alternately, divide popcorn evenly between mini plastic cauldrons or Halloween-themed treat bags and secure with ribbon or twist ties.