How do I get the tye-dyed effect with buttercream icing on my cake?

Do you want random color or to make lines/circle of color radiating out? I have not done it but I saw where the person used 4 different colors and piped large dots of icing out randomly close together and then used something to run the colors into one another some. Also I have seen colored gel being used to make the design. Sorry I can't help much, but maybe someone else could shed more light on it. The only thing was the design was not smooth it was textured. I don't know if you could use Viva to smooth it out without wrecking it.

I did a tye-dye cake that I thought came out awesome. It's in my photos. (seven lines down in the center)

I started out by writing the words I wanted far apart from each other. Then I used stuff in the kitchen, a glass, tupperware or whatever round items for different size circles to fit around the words. I also added a couple more starting points, not using blank circles but a little starburst of color. I used tip 18 (star tip) and zig-zagged a different color around each circle making it around 1/2 or 3/4 inch wide or so. Then I took another color and zig-zagged around the outside of the first color.

I took a toothpick and drew it back and forth between the two colors to blend a little. Then I went on with the third round ... eventually one round started hitting another so my circles were starting to become semi-circles; but I just kept going until the whole cake was filled in ... always drawing a toothpick between each two colors as they met each other.

I must admit it really worked up fast! I loved the results! I tried not to repeat the same patterns of colors around each cirlce.

I'll be happy to answer any further questions.