Can a park ranger stop to check your car tell you your inspection sticker is invalid because its the wrong color and bring you a ticket days later because he wouldn't look up the violation code?

Answer 1

I'm not certain that "park rangers" have any authority to check inspection stickers at all (side note: some sheriffs and highway patrolmen wear uniforms that might at first glance be mistaken for that of a park ranger, particularly by someone who isn't intimately familiar with the details and was in a place where they'd expect to see a park ranger), but if this isn't a completely hypothetical question and one did in fact do what you've described, then they probably do have that authority. You can challenge it, but you'll likely lose, so f your inspection sticker was, in fact, still invalid on the second visit, then you're boned; pay the fine.

If you corrected the sticker in the meantime, then by all means challenge it; you should win. If the sticker is valid despite being "the wrong color", then again, challenge it and you should have no trouble.