If in doubt, shake the crap out of all of them. S'cuse my language.
I've found that my ammonia results really depend on light and angle, sometimes dead yellow, others the faintest whiff of green ... Not even a .25. I'd cautiously say that as long as its only a tiny tinge, it might be residue left over from the last test or something. Remember to properly wash out your test tubes thoroughly not just a quick rinse. See if that helps...?