Why is My Pee Bright Yellow? Yellow Urine Causes & Symptoms 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 Yellow Skin (Jaundice): Causes, Symptoms, Prevention, and Treatment Options Meto blog