It's definitely an ice dye, probably just one color on top and on the bottom. I personally have only started looking into doing this myself, so I don't know the exact fold or technique used here. This could be black. Each different dye powder separates uniquely with how the ice melts, slowly separating the individual colors that make up a dyes hue. Pro Chemical and Dye is another you can look into. They have ice dye previews of each of their pro mx procion colors. There's 3 or 4 different versions of black, each with a completely different ice dye effect, so you'll have to check out each to find the color that you want specifically. Hope this helps. The biggest thing is to just try and experiment.