1. Spray a 10×15-inch rimmed baking sheet with nonstick cooking spray; line with a piece of waxed paper.
2. Place white chocolate in a heatproof bowl set over (not in) a saucepan of simmering water. Heat, stirring occasionally, until smooth, 4 to 6 minutes. Add food coloring and extract. Remove from heat; stir in rice cereal.
3. Transfer mixture to prepared pan; with a spatula, spread to edges of pan.
4. Sprinkle with crushed candy; with a piece of waxed paper covering the entire surface, press in gently (paper prevents hands from sticking to candy and chocolate). Chill until firm, 20 to 30 minutes (no longer, as candy will begin to soften).
5. Peel waxed paper off. Break bark into 2-inch pieces. Store at room temperature in an airtight container, up to 1 week.