Mix the cake ingredients according to White Cake Mix box instructions.
Separate the batter into 6 bowls. Designate each bowl to a certain color of the rainbow. The 'red' bowl should have the most batter, 'orange' should have a little less, and so on until 'purple' should have the least.
Using Gel Food coloring, blend primary colors to make secondary colors: Red, Red+Yellow=Orange, Yellow, Green, Blue, Blue+Red=Purple
Marvel at all the beautiful batter colors!
Prep bundt pan according to cake mix instructions
Carefully pour batter into pan, beginning with red, pushing it to the outside edge of the pan with a rubber spatula, following with orange, and so on, until you finish with purple.
Bake according to cake mix instructions for 'bundt pan'.
Leave cake in pan until cool enough to touch. Using small rubber spatula, gently glide it between cake and pan to loosen.