toi- i think that is the opinion of the radzyner rebbe in shittas harambam. teimanim also have such a minhag for more info see: http://www.tekhelet.com/guide.htm
patur- i don’t see any reason to assume domeh lrakia means green any less than domeh lasavim means blue. the mareh panim and tos. assume it is a machlokes . if it is not a machlokes than you have to be madcheh one of them. so why is green davka over blue?