SPRAY large mixing bowl with nonstick cooking spray.
HEAT marshmallows and butter in large, heavy-duty saucepan over medium-low heat, stirring frequently, for 5 to 10 minutes, until smooth. Remove from heat.
WORKING QUICKLY, pour the melted marshmallow mixture into the large greased bowl, mix well. Stir in 2/3 cup morsels into the cereal and marshmallow mixture.
SPRAY hands with nonstick spray. Press marshmallow mixture into 1/3 cup measure; then form mixture into an egg shape with hands. Repeat with remaining mixture to make a total of 24 eggs.
DIVIDE remaining morsels into separate colors. Place each color into small, microwave-safe bowls. Add 1 teaspoon oil to each. Microwave each separately on MEDIUM-HIGH (70%) power for 45 seconds; STIR. Morsels may retain some of their original shape. If necessary, microwave at additional 10- to 15-second intervals, stirring just until morsels are melted.
DIP end of each egg into melted morsels; shake off or scrape excess against side of bowl. Place each upright in muffin pans. Refrigerate for 10 minutes or until set. Store in airtight container.