I got told me quite the opposite, from people with actual medical degrees. That multivitamin supplements aren't all that useful since the body tends to not absorb much of it and excretes it. It's better to get the vitamins from your food.
If vitamins get fully absorbed why is my piss bright green when I take a multivitamin?
Me, I split my "One A Day" type vitamin/mineral pill into two and take one half with breakfast and lunch. I avoid dinner for minerals to give any excess the best chance of getting excreted during the day when I'm pushing a lot more water though my kidneys.
As for your problem ... are you sure that's not just some dye in the pill? I don't know of anything that would be "bright green" that you'd likely be taking.
If vitamins get fully absorbed why is my piss bright green when I take a multivitamin?