Fondant Rainbow Tutorial

This tutorial is on how to make a fondant rainbow. This not a cake topper, rather, is a 2D rainbow on the side of the cake.

I made this rainbow for a Rainbow in the Clouds themed birthday cake. This rainbow had all the 7 colors of the rainbow and turned out absolutely symmetrical. And I am also sharing on this page, my tips on how to mix the perfect rainbow colors for a fondant rainbow.

In fact, I used the same set of colored fondant to create rainbow letters for the cake (click here for the tutorial on how to make rainbow colored 3D letters for cakes).

How to Make a Fondant Rainbow

These were the main supplies I used for making the fondant rainbow:

Fondant - I used Satin Ice fondant in white, yellow, orange and baby blue. For the rest of the other rainbow colors, I used white fondant and tinted it with food coloring.
Food coloring - I used Americolor gel food colors in red, avocado, royal blue and electric purple (see below on how I mixed these colors to achieve the rainbow colors)
Extruder tool with medium-sized round disc - I would say this tool makes a lot of difference in ensuring the size consistency of each color strip and not forgetting of course, the time it saves in achieving the consistency.
White paper and styrofoam dummy - I drew the rainbow template (the smallest curve) on the paper and wrapped it around a 6-inches round styrofoam dummy to pipe the rainbow strips.
Shortening - I used shortening to attach the rainbow on my fondant covered cake.
Craft knife - I used this to trim the ends of the rainbow strips for an even finishing.

And this was how I assembled the fondant rainbow on my cake:

Mixing the colors

The first step was getting fondant ready in all the 7 colors of the rainbow. And this were the color mixes I used:

Red - White fondant + Americolor Red Red
Yellow - Yellow fondant + white fondant
Orange - Orange fondant + white fondant
Green - White fondant + Americolor Avocado
Blue - Baby Blue Fondant
Indigo - White fondant + Americolor Royal Blue (2 parts) + Americolor Red Red (1 part)
Violet - White fondant + Americolor Electric Purple.

Fondant arranged in a row, in the 7 colors of a rainbow

The rainbow template

Next was getting the rainbow template ready. The template was required only for the smallest curve on the rainbow which is the violet strip. I drew it on a piece of white paper.

A paper with a semi circle drawn on it. In the background are a round cutter and a long pencil

I then taped the paper around the sides of a 6 inch round styrofoam. Since I was going to pipe the violet strip on the template, to ensure it remains in place, I positioned two fondant containers on both its sides. I applied a little shortening on the paper so that it is easier to work on.

Attaching a paper to a styrofoam dummy with tape

Making the rainbow

Using my extruder tool, I piped out the last color of the rainbow, ie violet. With the help of my round cutting tool (which I also used to draw the template earlier on), I positioned the strip into a semi-circle on the paper, trimmed the excess and left it aside to dry for about 10 minutes.

A violet strip of fondant in a semi circle position on a paper template around a styrofoam dummy

Using a sugar craft knife to cut the excess of a violet strip of fondant

After about 10 minutes, the strip was not too dry but was able to hold its shape. I applied some shortening on my cake where I was going to stick the rainbow (with the guide of my round cutting tool earlier). And then, I gently lifted the violet rainbow strip and placed it on my cake (again with the help of my round cutting tool as a guide).

A semi circle strip of violet fondant held in hand. In the background is a blue cake with a round cutter on the side.

Using a round cutter to position a violet fondant strip on the side of a cake

Once the violet strip was in place, I went on with the rest of the colors. I applied shortening on the cake before each strip went on.
And after each addition, I trim off any excess with my craft knife.

Blue, violet and indigo fondant strips in the shape of a rainbow on the side of a blue fondant covered cake

Fondant rainbow on the side of a light blue fondant covered cake. The red strip of the rainbow is longer than the rest of the colors

This was how my completed fondant rainbow looked like on the cake.

Fondant rainbow on the side of a light blue fondant covered cake

For the finishing touch, I added fondant clouds at both ends of the rainbow. I have a separate tutorial on how to make the fondant clouds (click here to learn more).