Answer: The red at the bottom represents the base of the tube, not the red liquid.
Explanation:
The densest materials have more weight per unit of volume.
This means that those elements will always flow to the bottom of the containers, like the one in the image.
The red liquid being the least dense one, can not go to the bottom by its own means.
There could be some cases, like:
The red liquid when solid, is way denser than in its liquid phase, and then the red at the bottom could be solid phase of the red liquid, but there is no mention of this in the question, then we can discard this idea.
Another trivial idea is that the red liquid at the bottom could be trapped by some kind of wall, but again, there is no mention of this, so again we can discard this idea.
The thing that makes sense is that the red at the bottom represents the base of the tube and not the red liquid.
