My husbands toe nail is falling off and that two and the one next to it is blueish in color what could be wrong?

Not uncommon: If a runner, could have "blue toe" syndrome, if exposed to recent trauma (dropped something on foot) could be nails releasing because there had been separation of the nail from its "bed, " and new nail will grow from matrix at base. Other causes more esoteric and should be evaluated by dr / podiatrist.

Get it checked out: I would have this checked by a podiatrist immediately. It could be as innocent as trauma from shoes or the nail loosening due to fungus underneath it. Or it could be much more serious, such as poor circulation that could lead to gangrene if not treated.