Yellow thumbnail on my left and right hands

Patient: I have noticed that the thumb on my left hand has turned yellow in the past 15 days or so.The nail is almost all yellow and some of the skin further down the finger.On my right hand,the thumb is also slightly yellow but not nearly as much as the left.My other finger are normal.What could be the cause?I’ve been drinking some vitamin B complex suplements lately coz i was told that they help relax the muscles.I like to run a lot so i took those.Does that have anything to do with it?Thx