Taking B vitamin supplements can cause the urine to develop a bright yellow color, says WebMD. Many vitamin supplements include dyes that can also transform urine into a bright, almost fluorescent yellow color, although in these cases it is the dye, not the vitamins, causing the color change.
Urine is normally a yellow color. Dehydration can cause the color to intensify, producing bright yellow or even orange-colored urine, according to WebMD. Various foods can also affect the color of the urine. For example, consuming a lot of beets or blackberries can result in reddish urine. The normal yellow color of urine is caused by a pigment called urochrome, which is a degradation product of hemoglobin, an important part of the blood, notes Wikipedia.