Shortly following the inception of the H1N1 flu epidemic, we saw H1N1 flu mask designs evolve, and run the gamut from silly to fashionable to geeky; the latter describes this temperature-sensing, color changing mask.
Marjan Kooroshnia, a Swedish textile-design student, created three different style masks printed with a thermochromic ink that changes colors if a rise in temperature is sensed. In addition to the traditional surgical style, she designed a wrap around scarf, and a full face mask that senses temperature increases of the forehead as well as around the mouth.
I do see the potential of false temperature readings though. People may think you are sick and you may just be full of hot air :)