I am assuming they are what is called Lucky Bamboo. It is the most common type of houseplant bamboo. As for the yellowing, it most likely has to do with the fact there is either no water in there of the water hasn't been changed for a while. I would recommend first rinsing their roots with fresh water. Next add fresh water so it barely is below the top of the roots, but never use softened water because the salts in the water from the softner is deadly to plants. The water needs to be changed every week and if you plant isn't to far along it shouls start sprouting new leaves in a couple of weeks.
Operational Manager at
Earl May Nursery and Garden Center in Ames, Iowa