LINE 11 x 7-inch baking pan with foil. Set up 4 small, heat-proof bowls for quick color and transfer.
COMBINE sugar, butter and heavy cream in medium, heavy-duty saucepan. Bring to a full rolling boil over medium heat, stirring constantly. Boil, stirring constantly for 5 to 6 minutes or until candy thermometer reaches 225° F.
REMOVE from heat and quickly stir in morsels and marshmallows until smooth.
QUICKLY TRANSFER mixture into the small bowls, adding a dab of color to each one and leaving just a small amount in your pan to be uncolored and just plain white. All of this should be done very quickly as the fudge will set the more it cools.
CAREFULLY POUR each color into prepared pan, alternating colors, and swirl the colors all together while it’s still warm. Top with edible stars or sprinkles. Refrigerate for at least 2 hours or until firm. Lift from pan; remove foil. Cut into pieces.