Watchers have black blood, or alternatively and even cooler, void blood (think they type of thing grian is doing with his eyes this season)

Grian and pearl have to use the watcher power of changing how others perceive the world around them to make their blood look normal when they get injured around friends.

Watchers do not need to blink, so sometimes, they forget.

Pix is the worst for this, though its less forgetting and more he genuinely just hasn’t blinked in like 5 centuries or smth, like he closes his eyes and stuff, but he doesn’t just blink without actively thinking about it.

Pearl and grian also do this, pearl tends to forget more because years wearing a blindfold and then simply not needing it can mess up some habits, shes very embarrassed about it.

Grian also forgets sometimes also because of wearing the blindfold for years and then he sees someone else blink and realizes he hasn’t done that in a while and kinda does a bit of an exaggerated blink, he also exploits it to stare at people ominously.

Etho also forgets occasionally but he never wore the blindfold (he was only in the watcher realm for like a week before Grian hot him out) so why does he forget? Well he forgot to blink until his eyes were super dry before becoming a watcher, and now he’s a watcher there is no consequence to not blinking so he forgets even more.

Keralis also doesn’t blink, he is not a watcher, he is simply Keralis. It’s very possible that he does not have eyelids. Nobody knows

Grian has fluffy hair, not exactly curly but fluffy, Mumbo had very straight flat hair, but after the soul shenanigans in season 8 mumbo has the same hair type as grian.