Here is the process, if you'd like to make some yourself. I got the idea off pinterest, but used Ziploc Bags instead of bowls so the mixing/pouring would be easier.
I made cupcakes for all 3 second grade classes, so I mixed up 3 white cake mixes (altogether) and separated them into 5 gallon sized bags. I added about 1/4 tsp gel food coloring into each bag, then mixed.
I set out my foil baking cups, and started with purple. I put a little bit in each cup. Cutting off a small end of the bag made this process SUPER easy. Then I repeated with each color until my cups were 2/3 full and I was all out of mix.
Then I baked two pans at a time following the directions on the packaging. You can see by my mess that I was lazy and just squirted the cake mix into these pans. The others were easier because I used a baking sheet. (Foil baking cups do not need cupcake pans).
While they were cooling I went to the Y (March challenge: running 4 miles/5x week). When I got home I cut up these AMAZING candies (I think that's what really set the project off!) called Xtremes Rainbow Berry Sour Candy, made by Airheads. They come in long strips, and I needed a little less than half for each cupcake. If they are too long, then the rainbow will slip off.
I iced half of the cupcakes with green grass and half with blue sky. The clouds are whipped white icing. I added white edible glitter on the blue cupcakes and gold sprinkles on the green ones, to look like bits of gold.