When Joe Doucet bought a new house in Katonah, New York, he wanted to make it as environmentally friendly as possible. As a designer and inventor, he immediately found himself wondering whether the exterior of his home could play a role in mitigating the effects of climate change.

“One of the things I had not really considered before was: What color should I paint the house?” he told CNN, speaking in a video call.

Naturally curious, Doucet  started by 3D-printing small scale models of his house, complete with similar levels of insulation, and painting them in different colors. Over the course of a year, he found that in winter the inside temperature of the black model was on average 7 degrees Fahrenheit warmer than the white one. In summer, the white model house was 12 degrees Fahrenheit cooler.

“The answer wasn’t, ‘Should I paint it black or white?’ The answer was: It should be black in winter and white in summer,” he said of the findings. “It is not really feasible to paint a house twice a year. I began to think, ‘Surely there are other ways of doing this?’”

Doucet’s solution was inspired by his childhood interest in mood rings, which feature manmade “stones” that change appearance according to the wearer’s finger temperature.

After a lot of trial and error, he developed a kind of thermochromic pigment containing the crystals and started experimenting with a tin of ordinary housepaint and different additives. The result was a substance that could change color by absorbing ultra-violet light (which produces heat) above a certain temperature.

His climate-responsive paint, as he dubs it, appears “very, very dark gray” below 77 degrees Fahrenheit and gradually turns lighter as the temperature rises. Doucet has since filed a patent application for the technology.

But more than helping homeowners respond to rising temperatures, Doucet’s invention could have an impact on their climate pollution amid increasing energy costs and dependence on air conditioning (in 2020, 88% of US households used AC, up from 77% two decades ago).

Beyond the science, Doucet believes there is beauty in the idea that buildings might shift with the seasons, like the leaves on a tree. “There’s something poetic about seeing the built environment and the built world change with the seasons in the way nature does,” he said.

He also notes that new climate-responsive paints need not only change from white to black: “You can tint this pretty much any color,” he explained. A house could turn light blue in warmer months before turning a darker blue in the wintertime, he offered as an example.

It's a fascinating new advancement for something as simple a question as, “what color should I paint my house?”