Anila, if nearly the whole bag is green, you should take them back to the shop for an exchange (unless you've left them out somewhere in the light). Sometimes they get left in the sun in transit to the shop so they're green when you buy them.
usually i dont buy them if they are green, but every bag of washed baby potatoes was green, and sprouting, and i needed spuds and didnt have time to go else where.
But definatly never again..