[Musem1]

Being that I am not a chemist, my question may seem novice...but here goes.  I am working on an idea and to make it feasible I need to determine two chemical substances that would work together as an additive, and an activator. They would need to be nontoxic, and when combined, cause a color change in water. Kind of along the lines of the chewable tablets that are given to children to demonstrate the effectiveness of their tooth brushing.  The difference being that the effect in that case involves using a solid tablet. I am looking for something liquid.  In general I want to be able to mix the "additive" into a chemical product and apply it to something, and then later once it has dried, be able to mix the "activator" with water which would then be applied to the first item to produce a color change affect in the water carrying the "activator"

Is this possible? If so does anyone have any ideas for the two chemicals that could be used?

Again they would need to be fairly benign.