Hello Doctor, My Husband Has Been Noticing A Yellow Color

Hello doctor, My husband has been noticing a yellow color on his hands and a little on his feet. It looks almost like a stain that comes from leather gloves. He is 62 years old and had quadruple bypass surgery in 2010, but is very healthy. He had been eating a lot of pumpkin pie, sweetened with Xylitol. Would you know of anything that might be causing this?
Thank you, Melody