What could this be?

It's been on my wrist for a couple days now. It doesn't hurt or itch or anything and honestly wouldn't have noticed if it wasn't so dark. It would be different colors and hurt a little if it was a bruise, right? I don't remember doing anything that would have caused this. I've had a cold... show more It's been on my wrist for a couple days now. It doesn't hurt or itch or anything and honestly wouldn't have noticed if it wasn't so dark. It would be different colors and hurt a little if it was a bruise, right? I don't remember doing anything that would have caused this.
I've had a cold this week but thats all.
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