Why Your Pee Turns Bright Yellow from Certain Supplements First time taking a multivitamin. Urine is neon yellow and it's freaking me out : r Supplements Vitamin B supplements, especially those containing riboflavin (vitamin B2), often cause bright yellow or neon colored urine. This happens because excess riboflavin is water soluble and is excreted through urine when the body has Vitamin B supplements, especially those containing riboflavin (vitamin B2), often cause bright yellow or neon colored urine. This happens because excess riboflavin is water soluble and is excreted through urine when the body has Glutathione: Why is it important for detox & how to improve the amount in your body RealTime Laboratories Glutathione You Are The Healer