Snow dragons don't seem to be as popular as more colorful dragons. I have looked for them in the past (though where I live there is a far more limited number of morphs available, though translucent and silk/leather backs are now available..but never been a fan of the translucent myself and though the silkbacks and leathers are interesting, not really interesting in owning one.) but dont' see them for sale at the local reptile shows..or at last not in a 'pure' state. Most are part of the usual mongrel mix that seems more common up here.
Hypos are just dragons with reduced pigmentation (hypo basically means less, opposite of hyper), and for all I know, breeders over the years may have just started calling what would have been termed 'snow' ten years ago, to hypo, as the new 'morph'. Most pictures of white adult dragons I see now tend to be called hypos anyway...though I haven't paid all that much attention to dragon morphs.
Most other reptiles a 'snow' usually means they carry the trait of amelanism (albino) and anerythrism together...lack of both black/brown pigment and reds (and most yellows).
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PHLdyPayne