Its radiation can be shielded by Lead.
Its actually blue on the outside but there is a yellow light on the inside when light hits it it glows there for it makes green.
Effect on Kryptonians
When in proximity to Green Kryptonite, Kryptonians have displayed loss of their superpowers; weakness; nausea; pain; their veins pop out and look dark, and their skin also begins to turn slightly green after long exposure. Prolongued exposure to Green Kryptonite is fatal to Kryptonians.
Effect on Humans
While Humans will at first seem unaffected by this strange radiation, it does have discernable effects. Under certain types of intense exposure, Humans may gain superpowers through the effects of Kryptonite. In some cases, this lasts only as long as the human is exposed to Kryptonite; in others, the human may gain permanent powers or mutations. This last category becomes known as Meteor Freaks.
Also, as in the case of Lex Luthor, who wore a kryptonite ring, prolongued exposure to a subtle amount of Kryptonite radiation may cause cancer. Lana Lang, who wore a Kryptonite necklace in Smallville, has not yet shown any signs of this, however.