Hello,
What kind of chemical would be able to be put in water, in a see-thru tube, and as it passes a certain point, through some force whether magnetic or heat or something, it changes color. I mean it has to be visible color change.
The water is in a loop and needs to be able to change back and forth in color.. it doesn't necessarily need to be color.. maybe turns really murky or really dark or something.
Nothing can be added to the tube to change it after the assembly.. this colour change needs to be done by something outside of the tube.
