User blog comment:CureHibiki/Mahou Tsukai Pretty Cure! PV is coming~/@comment-25201298-20151227181632/@comment-25034020-20151229012948

I think the green may refer to Linkle Stone Emerald to be honest. Once they get the Linkle Stone Emerald, either that stone transfroms into "Emerald Style" or! The Emerald Style jewel is instead for the sixth ranger Cure, in this case the Green Cure.