The current Green and White stickers are valid until 1/1/19.
Thereafter, they expire and will no longer serve any use for drivers.
Any re-issued Green or White replacement sticker from this point forward will be valid only until 1/1/19.
Any vehicles purchased after Jan 1 2017 can apply for the next sticker color (Red) for use after 1/1/19 provided they meet the income eligibility AND they have not applied for the CA Clean Vehicle Rebate Program (CVRP) rebate (If you are under the income threshold, you can have both).
Summary - All White and Green expire by the end of 2018. Only new vehicles to the program which never before had HOV stickers can apply for the new Red, provided the income means test and CVRP requirements are met.
Vehicles models from prior to 1/1/17 can apply for the new Red sticker provided they have not had a prior sticker and meet the income/rebate eligibility discussed on the website above.
All remaining CA HOV stickers expire 1/2022.