change from color to opaque You mean change from color to transparent? For something to maintain any properties or transparency at 425C you're going to be looking for a ceramic - no polymers can survive that kind of temperature. I know some ceramics that change from transparent to opaque but generally not the other way around. Does it need to be reversible or can it be an irreversible transition? If all you need is for it to transition once you could use a dye within a transparent ceramic where the dye thermolyzes at 55C and leaves only ceramic. But once it's decomposed it's not going to return to its colored state.

Our two girls have gotten darker, i think in part because of our colder, rainier 'winter' this year.

https://www.mcmaster.com/content/pressure-sensitive-film

Placebo-itis is a common health hazard caused by things like this. Symptoms range wildly from no symptoms at all to lack of concentration, headaches, reduced judgement, back trouble, joint pain and digestive issues. Sufferers may also feel that the placebo substances act as a catalyst for positive and/or negative outcomes with other co-morbidities. Placebo-itis is a contributing cause of death in over 30% of those infected within 85 years. Disclaimer: I am not a medical doctor, psychiatrist or professional comedian. The above comments are there only to highlight the relative danger to human life span of coffee cup coatings compared to genetics, diet, exercise, lifestyle and bad luck. To the person drinking out of the cup the coating would have an unmeasurable health impact, but if that person was working in an unregulated factory sweatshop applying the coatings to thousands or millions of cups without adequate ventilation THAT could be dangerous.

https://www.google.com/url?sa=t&source=web&rct=j&opi=89978449&url=https://www.catster.com/lifestyle/cat-facts-genes-siamese-cats-temperature-sensitive-albino/&ved=2ahUKEwipj7-3_OeDAxXEkokEHVn-AhIQFnoECCYQAQ&usg=AOvVaw21FhsZlfx4CwjOWQUIb81F

The answer is **Thermochromic pigments change color with temperature, while photochromic pigments change color with light exposure.**. ☆**Question 2:** Step 1: **Define thermochromic pigments.** Thermochromic pigments are materials that change color in response to temperature changes. For example, a thermochromic mug may appear black when hot and change to a different color, such as white, when it cools down. This property is often utilized in products like mood rings and temperature-sensitive labels. Step 2: **Define photochromic pigments.** Photochromic pigments are materials that change color when exposed to light, particularly ultraviolet (UV) light. For instance, photochromic sunglasses darken when exposed to sunlight and return to a clear state when indoors. This property is commonly used in eyewear and certain types of coatings. Step 3: **Summarize the differences.** The primary difference between thermochromic and photochromic pigments lies in their stimuli for color change: thermochromic pigments respond to temperature changes, while photochromic pigments respond to light exposure. The answer is: **Thermochromic pigments change color with temperature, while photochromic pigments change color with light exposure.**