cover the cake with white fondant. Then cut a cirlce about 3" bigger than the cake diameter. Use a cutting tool or cutter to get the wavy look with the yellow. Place it on the white and smooth out. Then you can roll a long thin sausage of blue and purple or use an extruder gun to make a long rope/snake shape. Use water to keep it in place as you guide it under the yellow wavy line.
There are two ways to achieve that look. Layering and putting strips.