Here, on the Campbell River beaches, so far, I have seen mostly purple shore crabs, like this one:
|Young purple shore crab, Hemigrapsus nudus.|
Since the greens can be purple, and some of the purples are green, they are hard to distinguish at first glance. But the purples have those pretty red or purple polka dots on their pincer arms; the greens don't.
And this one has sparkly green eyes, to boot. Handsome, isn't he?