Baking · Cake · Desserts

Rainbow Happiness Six Layer Cake

We had the mother of all rainbow birthdays this weekend for my sweet six-year-old Madison. My house looked like a unicorn threw up all over. It was epic fun. A hyperactivity inducing, spectrum spectacular. Brightly colored craziness. We had a blast. The pièce de résistance of the party was a stunning six layer rainbow cake. It was truly a sight to behold. It requires a bit of time, but is totally worth it for an awe inspired gasp from your guests when you cut it open.

First of all, the food coloring you use is going to greatly impact the boldness and ease of coloring your batter. I used Wilton gel colors. They are awesome.

I made three boxed white cake mixes, substituting melted and cooled butter and whole milk for the oil and water. I then separated the batter into six bowls and set to making a rainbow of colors. I ended up with 1 3/4 cups of batter in each bowl. I had a little bit left over that I left uncolored and made 8 cupcakes out of.

Here’s the trick for getting a red that’s truly red, not some version of pink. It’s totally counter intuitive. Start with pink coloring. Yes, that seems totally backwards I know. Use pink to make it un-pink? Trust me. Color your batter pink, then add the red coloring. Otherwise, you use a ton of red just to make it a pinky color. Pink first, then red coloring and you’ll get a finished product that’s a gorgeous red.

Grease and flour as many 9 inch cake pans as you can get ahold of. Cook the cakes two at a time at 350° (about 15 minutes). Don’t worry if the outside gets a dull color, the inside will still be vibrant. Cool about 5 minutes in the pan then turn out onto a wire rack to cool completely. I place some waxed paper over the top of each pan before flipping them out so that the wire rack doesn’t dig into the soft cake. When cakes are all cooked and cooled, trim (if needed) to flatten out the tops. Eat the bits…you know, to check for poison.

At this point, you can wrap each layer and pop them in the freezer. They’ll keep well for at least a week if you want to be super prepared and have the cakes made well in advance.

When you’re ready to assemble your cake, start with the purple layer and add a thin layer of frosting, then place the blue layer on top, continue with each layer, spreading a thin layer of frosting in between each layer until you have all six layers stacked. Gorgeous already!

Now we’re going to do a crumb coat to lock in all the little bugger flecks of multi-colored cake bits. Slap frosting on there. All over all the layers. Don’t worry about making it perfect. We’re going to go over the top of it. This is the ugly layer. It looks like my cake has a bad case of chicken-pox.

Put your cake in the fridge for about 30 minutes to solidify the crumb layer. Then pull it out and frost it again. This is the pretty layer. I use an offset spatula. Let it set for about 15 minutes, then rub a paper towel around the outside (lightly) to smooth out any little bumps.

I decorated the exterior of my cake with a layer of Skittles (and blue M&Ms) around the top and bottom. Then a rainbow on top with puffy marshmallow clouds. I used clear piping gel to stick the marshmallows on. I printed off a rainbow coloring page and traced the outline of the rainbow with the piping gel, then set it lightly on the top of the cake, transfering the outline so I could make a perfectly arched rainbow by following the lines. Yes…I cheated. And you can too. There are people who can do amazing things like cut in a straight line and place perfectly arched rainbows freehand. I am not one of those people. I buy the wrapping paper with the grid lines on the back, and I’m not ashamed of it.

My sisters were over to help with the decorating (because I’m craft challenged) and they helped me put the finishing touches on this cake. We didn’t have the idea to airbrush some sky blue on until AFTER we’d placed all the Skittles. You can save yourself a lot of trouble by doing this step first. Using the airbrush color cans you can get at any grocery store, spray the top of the cake a light blue. Use a pie crust cover to block the color from ending up all over the sides of the cake.

This cake is gorgeous on the outside, but the real beauty lies within. Just like my sweet daughter Madison. Who thinks I’m pretty much the most amazing mom ever. At least today after experiencing the rainbow wonder of this cake. 🙂 Notice the tiny finger mark? There were 18 kids at my house yesterday…I have no clue who the culprit was.

Using a very large knife, cut this into slices and transfer to large plates. Take a moment to stand in awe of the masterpiece before you.

Six layers of amazing. Seriously.This cake makes me so happy. I can’t even stand it. It is simply stunning. And delicious. You won’t believe how elevated a cake mix tastes when you swap out oil for butter and water for whole milk. The cake is light and fluffy, super rich and scrumptious.

My husband commented that this cake was so beautiful it made him want to eat it. And he hates cake. Wierdo. It really is a looker.

Enjoy the happiness of this cake! You could easily do a variety of colors if you (or your munchkin) aren’t into rainbows. Dr. Suess? Fourth of July? Team colors for an end-of-season event? I’d love to see what you all come up with!


Print Recipe for Rainbow Happiness Six Layer Cake

Rainbow Happiness Six Layer Cake
idea from Pinterest, specifically here

Three boxed white cake mixes
Ingredients per the box – except use butter (melted and cooled) and whole milk to replace oil and water
Wilton Gel Food Colors
Two batches Crusting Buttercream (recipe below)

Prepare batter per box instructions and separate into 6 bowls (about 1 3/4 cups of batter per bowl).
Color bowls red, orange, yellow, green, blue and purple.
Grease and flour 9 inch cake pans. Bake at 350­ degrees for 15 minutes.
Allow to cool then assemble starting with purple at the bottom.
Layer frosting between each colored layer then coat with a crumb coat of frosting.
Allow frosting to harden in the fridge for 30 minutes then frost again. Decorate as desired.

Crusting Buttercream

from Cake Central

2 lbs. sifted powdered sugar
1/2 cup or 1 stick butter, softened.
1-1/2 cups solid vegetable shortening (Crisco)
2 tbsp. clear vanilla extract
1/3 cup water for icing cake -OR- 1/4 cup for stiff consistency (for a more flavorful frosting, use milk)
1/4 tsp. almond extract


Cream butter, shortening, and extracts until creamy and smooth. Gradually add powdered sugar and water. Mix thoroughly on medium speed for hand mixers, low-speed for stand mixers, until smooth and creamy. Do not overmix or mix on high-speed.

For stiffer icing, use 1/4 cup of water instead of 1/3 cup.
If you live where it is humid, you can add 1-2 tbsp. meringue powder.
Let set for 15 minutes before smoothing with a VIVA paper towel.
Icing can be refrigerated for 2 weeks in an airtight container. Iced cake can sit at room temp. for 2-3 days.

*Any flowers made with this recipe remain soft enough to be cut with a knife.


28 thoughts on “Rainbow Happiness Six Layer Cake

  1. Very Beautiful cake!!! I am planning to make the cake 3 days in advance and freeze (as your suggestion till one week should be fine) it. Should I defrost the cake before I put the frosting? if yes, where should I defrost, over room temperature or refrigerator and how long? Thank you so much.

    1. I always just take my cakes out of the freezer and start frosting immediately. I don’t let them come to room temp. You’ll keep the crumbs away more the colder the cakes are.

  2. Why did u replace the oil and water with milk and butter? I was just wondering if it bakes better, tastes better, or if its just something you do:) thanx for the awesome cake I cant wait till my daughters birthday!!!

  3. HI. I am loving this cake and would love to make one for my little boys third birthday. Question, is it possible to make this cake with only one cake tin or possibly 2? Mix up all the colours into containers then bake one layer at a time storing the coloured batter in the fridge before baking


    1. Yes, you can make it with as few pans as you like – then you’ll just have to be cleaning cake pans in between. I’m too lazy for that. 🙂

  4. How many people does this cake serve? This looks amazing! Also when you swap the melted butter and milk, do you swap out for the same measurements that the water and oil ask for?

    1. Depends how much of each slice you give out. I cut the layers in half — each person got a piece with only 3 colors. It served about 24.

    1. Whatever measurements your boxed cake mix calls for. Just sub out the oil for butter and the water for milk.

  5. My little one Hannah is 6 I had to learn to make a Barbie cake. now she saw this one and I need to make one of these now LOL. Late but best wishes hope she had a great day.

    1. I know the feeling. I do everything possible to keep my kids away when I’m checking Pinterest. They ALWAYS see something I just HAVE to do for them. LOL.

  6. Looks awesome! If I start making this the night before, can I frost, and leave on the counter and just do the M&Ms the day of the party? Or can I puthe M&Ms on and leave the fnished cake out on the countertop the night before? I am worried about the color bleeding or M&M slippage…

    1. I put the m&m on the night before and then put it in the fridge. Don’t remember there being any color bleed. Probably would be if the frosting got too warm though.

  7. hi.i want to make the rainbow cake in a 10” cake many cups do I need per layer?you used 1 3/4c….will 2cups do?and how much frosting you think I will need?thanks

    1. I’d really have to make it in a 10″ to give you an exact. I’d guess 2 cups would be about right. Just be sure each layer is about half full. Maybe try one layer and see how much it needs before coloring the batter for the rest?

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