Hello, I have a friend who wants me to make her this cake for her birthday and I have no idea how to make it. The photo she sent me is from craftsy. 

I have no idea how to make each slice a different color. Do I have to make a million different cakes then cut them up? Please help :(

Wow, would she be happy with that on a smaller scale with less colours?  That's a lot of baking.  I'd make a huge batch of white cake, and colour each portion individually.  I don't see how it could be done any other way.

Wow!  I also wouldn't want to make that much variation of color, however.....if I WERE to it, I'd  make the white cake( it would take more than one batch) and color it three ways...one third red, one third blue and one third yellow.  then from that I could mix one layer at a time by mixing two colors in progressively more proportions. For instance, starting with red and yellow, pull out maybe 2 cups of the yellow and add 1/4 c. red for the yellowest orange  and bake that layer.  The next layer, pull out 2 cups of the yellow and add 1/2 cup of the red for a in-between orange and so forth. 

It would be a total pain where I sit down, and I would campaign strongly for just primary and secondary colors.   If she wants the total length, you could make 2 torts  of each color, that way you could bake a full layer of each color and tort.

My Guess.  There are 30 color variations to this cake.  If you divide that by 5, that's 6 colors in one batch (I assume they used white cake mix).  So five cake box mixes, each one divided into 6 bowls to make colors in succession.   

I have never made a rainbow cake so.....

AAny chance you could go to the Craftsy website, buy the tutorial, and learn the best way to do it? The Craftsy instructor probably has tips and trick to make it easier and more efficient to do. That would be my suggestion.

When I first looked at the cake I pictured my 16 inch loaf pan, and then when I saw the colors inside

I thought it would be easy to color the batter and put layers of batter In that long pan.  Then each person would get a slice of the rainbow.

But that photo is a CUSTOM HIGH END expensive over the top FABULOUS cake. 

Thank you to all you fantastic people here on cake central. I really appreciate your comments and help.

AHere is the link to the woman's flicker account. She tells how she did it in the comments, toward the beginning.

[URL=http://www.flickr.com/photos/emily-weaver-brown/4827840735/]http://www.flickr.com/photos/emily-weaver-brown/4827840735/[/URL]

I am glad I pinned it a long time ago, before people pinned only the picture

I'm pretty sure that's not from a Craftsy class, I bet it was featured on their blog...

They've done many posts (some written by well known cakers...Lesley Wright - Royal Bakery, for one) that are just a round-up of cakes made by different people but fit the particular theme for that post...

Edited: Yes...here it is: http://www.craftsy.com/blog/2013/07/colorful-rainbow-cakes/

If you follow this it takes you to step by step pictures how to make it.  The key is having the right cake tin which is a muffin tin that you can bake 8 small cakes at a time.  Clearly time consuming but relatively simple when you know how.  My computer skills are not up to my cake baking skills so I don't know how to make this into a link, if anybody else out there can do it, please do.

http://www.chocolatesuze.com/2009/12/04/20-layer-rainbow-cake  

Hey my link worked booyah!

Thank you everyone for your help and suggestions ;)

Its nice to know people are out there that are willing to take the time to help out.