This is the Rainbow Cake that appeared in the Martha Stewart show as created by blogger Whisk Kid. It's soo pretty that I had to make one as well, with tweaks of course. Which I found out later had very different results from the above cake. I included pictures of how the cake should look like for perspective.
1st variation, the cake batter was separated using a ladle instead of weighing individual bowls.
2nd variation, I used food flavouring with colour instead of pure food colouring. Grape for purple, Blueberry for blue, Honeydew for green, Pineapple for yellow, Peach for orange and Cherry for red. Of course the blueberry turned out purple *oops* and the dark purple turned out a dull purple after baking.
3rd variation, I used cream cheese icing instead of lemon buttercream. It's a matter of personal preference.