Keep the Steel Man away from your tea party. What better way to insure that your party won't be interrupted by Superman? Just print a bunch of these and place them around your living room and surely you won't have any unexpected visits from Superman.
Print the kryptonite.stl with transparent or translucent filament, green, transparent or natural (PLA) should be perfect. I used PET for my print as it was the only transparent filament I had. Grey filament for the rocky base and if you so desire, print one of the inserts (the second one is ticker, to make for a darker green and easier to slice) in a green color and place it on the inside of the crystal, this should allow for a bit of green to shine through if you decide to use transparent filament. Most tea lights, at least those that I have, are yellow, so the green insert helps insure that the kryptonite stays greenish.