The first three rooms are white keys, the last three are black keys. You are looking for a black key right? Another tip is to run into the room to the bottom dragging most of the stuff with you and click your ticket. Then be sure you are killing ALL the vortices in the room(not just the respawns over and over). There is only one key at a time. I had an issue just after kr was released and the black keys on the vortices were not lootable and did not have a timer, which was not cool. So if you are seeing black frags and can't loot them then the keys are bugged. Shimmer is my favorite keyspawn. Most of the time I can finish it in about the same amount of time as mel keys. The best advice I can give is don't be afraid to use your ticket liberally.