There's a video of an astronaut putting a droplet of food coloring into a blob (sphere) of water on the ISS. The water turns the color of the dye almost instantaneously. On Earth that dye would slowly diffuse (I think diffuse is the proper word) into the volume of water. Why does it happen so fast in zero-g? I would assume this is simple Newtonian Mechanics. More specifically Fluid Mechanics. Does the dye even penetrate the surface of the water (surface tension)? Perhaps it just envelops the sphere of water?
The video is titled "4K Video of Colorful Liquid in Space" on NASA Johnson's YouTube channel.