So where am I going with this?
The answer is photochromic clothes. A company called Photochromia have developed a way of inserting photochromic materials into ink used to print onto hats, T-shirts and trousers so now your clothes can change colour when you go outside. Unlike Global Hypercolour (anyone remember that from the 90s) which reacted to heat, therefore showing where and how much you were sweating (ew!) these clothes will react to UV light.
Whilst the designs may not be to everyone's tastes I think some of them are quite funky, especially the idea behind Schrodinger's cat, and it is an interesting use of the technology, it's definitely a whole new take on the term wearable technology. You can read more about it and buy the clothes via their kickstarter page which has reached its target so the clothes will be made. Who knows what designs other companies will come up with and where it will go from here?