Final answer:
The food coloring molecules spread out and become evenly distributed throughout the warm water through diffusion.
Step-by-step explanation:
When food coloring is added to warm water, the molecules of color undergo a process called diffusion. The molecules spread out from an area where there are lots of molecules to an area where there are fewer molecules. Over time, the molecules of color will become evenly spread throughout the water, resulting in the water becoming an even color.