RE: Vitamin B Complex
It's Riboflavin (B2) that makes your urine neon yellow. Interestingly, riboflavin can aslo be blue, red, or clear. I'm glad it doesn't come out of ME in those colors, though!
B vitamins are water soluble, so your body can't store them. If you get too much, they just passes on to your kidneys.
The RDAs are estimates, some people will need more, some less. The reason people take megadoses is to make sure they get more than they need, no matter how much they do need. Some people think that super high doses of vitamins have other benefits, but I don't think this is really turning out to be true in actual research.
Personally, I take a regular multivitamin without Iron.