Heat color changing cup, can it be used Shabbos?
Answer:
It is permitted to use such a cup (or other utensil) on Shabbos, since no intrinsic change occurs in the object. Furthermore, no dye or coloring is applied to the utensil, and the change in color is simply a temporary chemical reaction to external temperatures.
For sources please see here concerning transition lenses on Shabbos.
This answer applies to a change of color, and not to the appearance of writing or pictures.
Best wishes.
