The Skin On My Daughters Fingertips Is Yellow/ Brown In

the skin on my daughters fingertips is yellow/ brown in color and seems to be a little thicker. It doesn't hurt or itch. She has had it for years. Dermatologist we saw had no clue. She doesn't smoke, use self tanner or hair dye. My mother had scleroderma but this does not seem like that. She is healthy, 22 year old athlete so no other Heath or vascular issues.