Heat semisweet chocolate pieces in a heavy medium saucepan over low heat, stirring constantly just until melted. Stir in peanuts. Spoon by rounded teaspoons onto a parchment or waxed-paper-lined baking sheet.
Heat vanilla-flavor candy coating in a heavy small saucepan over low heat, stirring constantly just until melted. If using, heat green candy coating in a similar manner. Drizzle a small amount of each candy coating atop each cluster, swirl gently with a toothpick to create a marbled effect.
Chill candy about 30 minutes or until firm. Store tightly covered in the refrigerator for up to 3 weeks. Makes about 24 pieces.