Tie-dye makes me think of the psychedelic 60's and 70's. Crazy, colorful, and carefree. I remember making tie-dye shirts when I was in Girl Scouts. I thought it was cool to be able to create something to wear myself.
The tie-dye effect can be created using any colors you desire. I think three colors work best. Working with six colors was challenging. I didn't like that the red started to harden before I had all the other colors on the cookie. I wasn't able to get other colors into the legs and horn due the unicorn shape. Simpler shapes (circles or squares) work better for this technique. I used this cookie cutter to create this cookie. I made all six colors of icing the red and purple were 15-second icing and all the other icings were flooded. I piped the colors on the cookie and then used my scribe tool create the swirl effect. Around the mane I tried to swirl the icing to look like a mane - it kind of worked.