Divide batter into 6 small bowls, about 3/4 cup batter per bowl. Add red, orange, yellow, green, blue and purple gel food colors, one to each bowl; mix. Pour each colored batter into a decorating bag or resealable food-storage plastic bag, and cut one corner off each bag. Starting with purple batter, carefully squeeze a thin diagonal line of colored batter onto each pan; repeating with blue, green, yellow, orange and red to make a rainbow-striped pattern. Continue until all batter has been used and pans are equally filled.