This is pretty cool too: 2-toned lobster

That is pretty awesome!

The wiki page that talks about blue lobsters mentions other lobster mutations, including the two-tone one, but only the blue one is pictured.

And apparently the two-tone mutations can take several forms. Check this one out. I find it simply amazing how precise the separation of colors is, but that National Geographic story says the two halves of the lobster grow independently, and given all the organizing forces present in development, I guess it shouldn't be all that surprising.

I think arthropods have spiralian development, which I think means that there's not a left-right axis until fairly late in zygote development. Which means that it's not as simple as knocking out one of the pigmentation genes at the two-cell stage. Which means that it must be a regulatory gene thing, and I don't know nearly enough embryology to guess how (or, indeed, why) the left side would get completely different regulation than the right side.

Whoops, not even close. Arthropods display idiosyncratic cleavage along with the rest of the higher ecdysozoans: Cleavage patterns and the topology of the metazoan tree of life. (Really interesting paper!)

The classic spiralians are the eutrochozoans (e.g. annelids and molluscs), over in the other big protostome branch.

Best caption ever: "The Blue Lobster receives it's characteristic name from it's blue color."