'Opaque Ranger Key' are those I call that are all one color, these are only Super Megaforce Rangers. Red, Blue, and Silver came available in Halloween costumes and boy underwear. Pink was only found in Halloween costume and Yellow has only been known to be handed out at Nick Hotel event in October 2014. It could've been handed out elsewhere. The Red key was handed out at Comic Con and Power Morphicon. Anyways, the Green, Red and Blue keys have been spotted at a Meet and Greet event via Cartoon Network Asia in the Philippines and probably other Asian countries. The Green Key was not seen before this. Technically there are all six Rangers now.
Photo Credit: @X_pacaud of Instagram