What You Did
You made art. You were able to observe the normally invisible interactions between two substances by adding food coloring.
When you added the soap to the milk, the colored milk started spreading all around the plate. The soap breaks down fat molecules and pushes them away from both the soap and water.
This experiment worked well for me the first time, but I could understand someone might forget which end of their swab had soap on it.
Change the amount of dish soap or use something other than a cotton swab to apply it. Try using a different kind of dairy: non- or low-fat milk, half and half, or heavy cream
hydrophilia/hydrophobia, unconventional art