Sharpie markers may not be soluble in water, but they are soluble in rubbing alcohol. Use this property to your benefit to create some wearable art (and science)!
dropper, drop rubbing alcohol into the middle of the ring.
The alcohol will move outward, through capillary action, and carry the ink with it.
If the ink is made of a mixture of colors, you will see the colors separate. If it's made from a pure color, you will simply see the color radiate outward.
Move the shirt on the box and make another pinwheel.
...try making your ring of dots with a variety of colors
...what happens if you make your dots in a shape other than a circle?
...what if you start with one central dot?