There's 2 possibilities:

1) The crops aren't done yet (they will be sparkly when they are finished)
2) Your FC leader hasn't given you permissions to harvest the crops. By default only the FC leader and I think FC officers are allowed to harvest.

If it's the 2nd case and your FC leader isn't able to be on super often you may want to let them know to give other people permission to harvest as time still ticks when crops are done and they will eventually die if not harvested.