Pour cereal into a very large mixing bowl and set aside.
Melt white chocolate, peanut butter, and butter in microwave. Heat at 50% power for 30 seconds at a time, stirring in between each time (chocolate scorches easily, so be careful!), until everything melted.
Pour mixture over cereal. Mix well, but gently (try not to break too much cereal). Spread out onto two large cookie sheets (use parchment paper if desired to prevent sticking) and allow to cool for 15 minutes.
Divide cereal into 4 parts.
Take 1/4 of total mix, put in Ziploc bag, and toss with between 1/4 & 1/2 C. powdered sugar, until well-coated. May have to unstick larger clumps. Spread out onto separate sheet to finish drying.
Melt pastel pink candy melts (heat at 50% power for 30 seconds at a time, stirring in between each time). Take another 1/4 of cereal mixture and pour melted pink candy over it. Stir with spoon until well-coated. Put in Ziploc bag, and toss with between 1/4 & 1/2 C. powdered sugar, until well-coated. May have to unstick larger clumps. Spread out onto separate sheet to finish drying.
Melt pastel green candy melts. Take another 1/4 of cereal mixture and pour melted green over it. Stir with spoon until well-coated. Put in Ziploc bag, and toss with between 1/4 & 1/2 C. powdered sugar, until well-coated. May have to unstick larger clumps. Spread out onto separate sheet to finish drying.
Melt pastel purple (or another color of choice) candy melts. Take another 1/4 of cereal mixture and pour melted candy melts over it. Stir with spoon until well-coated. Put in Ziploc bag, and toss with between 1/4 & 1/2 C. powdered sugar, until well-coated. May have to unstick larger clumps. Spread out onto separate sheet to finish drying.
After a couple of hours, toss all four colors together, along with the M&M’s. When well mixed, pour into mixing bowl. Serve. (Stand back and wait for compliments!)
Notes
Merkens is the absolute best quality candy melts. Trust me, I’ve tested them all. You may have to order them online. If you can’t get them, Wilton is second best. You’ll have to thin them with paramount crystals or a bit of shortening, though.