Fresh mussels, or are they?
Captured longer ago or not, should not make a difference. When you buy mussels, they are still alive. You can check this by trying to open one. Normally, this isn't an easy task. (Sometimes, their shells can open/close when opening the package in which they came in.)

The left hand mussel doesn't look tasty, but there really is nothing wrong with it. It's just a smaller size mussel. If you buy bigger mussels (e.g. Jumbo), you shouldn't have many of those in it.

As for the colour: a lot of people think this is a matter of sex. Males are white, females are orange. However, this isn't true. The difference in colour is a genetic one, it's the quantity of pigment a specific mussel has. The difference in colour doesn't make a difference in taste or texture.

Shortly: that mussel on the left hand side is okay to eat.