There's (blue) light at the end of the tunnel.

Here's something I didn't know: the lights in the toilets at the pub over the road from my work are blue apparently because blue light makes it harder to see your veins when injecting drugs. This is what I was told. I thought it was just energy saving or something...

So, now I want to know what else I don't know that I should? Answers on the back off postage stamps only please!