Merino wool, like everything else, fades over time, even in direct sunlight. Although Merino wool is slightly more prone to fading than other materials (following the same principle that human hair lightens in the summer), all clothing fades in principle in sunlight. However, since our T-shirts are worn more often and for longer periods of time, they also fade faster. A cotton T-shirt is worn for one day, then sits in the laundry basket for a week or two, so there's a natural limit to how many times you can wear it over the course of a summer. A cotton T-shirt will also fade in the wash before it fades in sunlight, so you won't see it there either.
Some people actually appreciate the fading and the life the garment gets, much like jeans do over time - and they use T-shirts for more than just pretty wear.
You can re-dye T-shirts with most textile dyes for cotton, following the instructions on the package, Dylon from Matas for example.
If it has been worn a lot and is a year old, it is not a T-shirt we can exchange for a new one. However, if you find that a brand new one fades in a short period of time, we can of course do something about it.