According to a CP memo that went out to the outlets: the green one is used IN ADDITION to the white one where the declared value is $500 or more. The insurance maximum is still capped at $100.
It doesn't really matter which sticker you use. If you still have green ones left, use them up. From a customs stand point, there is no difference between the forms. The only reason for the change is better documentation and proof in case you file an insurance claim. As long as you still have your cash register receipt while you use the green sticker, the insurance is still valid.
Lincoln