Thanks for the reply.
Yes, i have searched Google and Youtube, and it's explained how to make the clock reaction by turning transparent to orange, then orange to black.
There is also a version how to turn transparent to black.
Then there is another version, with indicator, to turn instantly into pink (without delay).
They all do not fit my needs.
What specifically i need, is to turn transparent to red-wine-color, and do it after x seconds.
I can use only 2 plastic bottles (with transparent liquids inside), and those bottles will be mixed. What should be in those 2 plastic bottles, to obtain this effect?
For the delay, i think it's just to add water to one of the bottles, correct?