1. Spray a 9inch square pan lightly with cooking spray, then line it with a double thickness of foil (this will make it much easier to lift out of the pan later) with ends of foil extending over sides. Spray lightly again and wipe out any excess spray with a paper towel.
2. Place semi-sweet chocolate chips and food coloring in a heatsafe bowl. Set aside.
3. Bring sugar, butter and half and half to full rolling boil in 3qt. saucepan on medium heat, stirring constantly. Cook 4 min. or until candy thermometer reaches 234°F, stirring constantly. Remove from heat.
4. Add white chocolate chips and marshmallow creme; stir until melted. Add vanilla; mix well.
5. Immediately, transfer about ½ of this cooked white chocolate mixture to the bowl you prepared in step 2.
(The white chocolate mixture will be very hot and will melt the dark chocolate chips). Stir well with a strong handled spatula or wooden spoon until chocolate chips are completely melted and incorporated.
6. Working quickly, with two clean medium size ice cream scoops or 2 tablespoons, plop scoops of each mixture
in a random pattern into a prepared pan.