Maine lobsters are usually greenish brown or black in color, but can also be blue, yellow, red or even white. The color of a lobster's shell does not affect its flavor or texture.
Look for lobsters that move around and hold their claws upward and their tails straight. Claws should never hang limply and the tails should never curl underneath its body.
Black marks or holes in the lobster's shell are the result of wear and tear and usually indicate an older lobster that hasn't recently shed its shell. Marks are not harmful in any way.
Hard Shell Lobster:
Hard shell lobsters have been living in their shells for quite a while, and so they're usually fuller. However, it requires the use of utensils to gain access to the meat.
New Shell Lobster:
New shell lobsters have recently molted and are growing into their new shells. Many people think new shell lobster meat is sweeter and more tender than the meat of a hard shell lobster and it is significantly easier to remove from the shell.