When I used to spray tan (yes, sadly I used to spray tan), getting the hands and feet to look natural was very difficult. I would put the barrier cream all over my hands, feet, and nails, but my nails and toenails would be stained brown. It looked like I had dirty toenails that I never cleaned. There was no getting the brown out of the nails either, you had to wait till they grew out.
Thanks to break.com for the pic.