So anyone care to explain how this works? Because my current best guess is me assuming that it has to do with each dye having a different viscosity or density or property that affects how far it "rolls" before stopping.
I'm pretty sure that each dye has a different viscosity, so the drop is a specific size, and each opening is set to be just greater, with each opening increasing in size. So Red has very small droplets, so the hole is small, while black has big droplets that wouldn't fit in the red size hole and roll past it until it gets to the black hole which is big enough. Similar to a mechanical coin sorter, I think.
The density/surface tension. Least on the bottom, most on the top. Like things will meld, and until it hits something similar the drop will just drop down
You can see the droplets bounce on the wrong color, so I assume it has to do with that the different colors are insoluble. This results in that they continue if they come upon the wrong color.
My guess is the gap between liquids is close enough that they touch- and if they are the same, the bigger blob of liquid absorbs the smaller one. Otherwise, it isn't held strong enough, and it keeps rolling.