Melt about 1/2 cup (see notes below for quantity changes) white candy melts according to the package directions.
Mix cereals and pretzels (and any other mix-ins that will not melt) together in a large bowl.
Drizzle 3-4 Tablespoons of the melted white candy melts over the bowl of dry snacks, and mix really well until the snacks have an even coating. Pour coated mix onto a large baking sheet and spread into a thin layer.
Melt additional colors of candy melts (in your choice of colors) and add a single color into a disposable pastry bag (or thicker ziplock type bag) and drizzle melted candy over the baking sheet of snacks. Repeat with another color as desired.
While the candy melts are still warm (and drizzled over the snack mix), add sprinkles of your choice all over the mix. Add additional mix-ins, as desired.
Allow mix to cool on a baking sheet until the candy melts have firmed up. Meanwhile, dip a few additional pretzels into any remaing melted candy melts, and top with sprinkles if desired. Lay dipped pretzels on a sheet of parchment paper to cool, then once fully cooled (and firm) add dipped pretzels to mix.
Package mix as desired, and enjoy!