It could be that everyone knows this already, but I just discovered something neat. Purple eyeliner makes my pale greenish-grey eyes look green. Like, really, properly green.
I've been meaning to try this since the time I had a black eye a few years back. As it healed, it developed an intense reddish-purple line along the upper lid, and several people commented on how green my eyes were. I thought it would be worth getting a purple eyeliner (red seemed a bad idea) to see if it would mimic the effect. It does!