My Space Grey Aluminium case Series 5 Apple Watch which I bought on December last year have so many discolouration around the aluminium frame at every sides. I have been wearing it with a case on ever since I bought it. It really makes me frustrated that I cannot even wear it without having the case on because it looks so awful and worn out now. I have never dropped it or hit it against the wall or something, and even with a case on the aluminium still discoloured terribly. I've seen quite a few people who have encountered with this issue as well not only on the watch but also on Macbooks.