Chris is closest to overcoming this problem, which is not white finger, it's caused by overworking the muscles and tendons in the fore arm running down to the fingers.
If you don't take remedial action you could end up with a condition known as carpal tunnel. Doctors will tell you an operation is necessary to resolve this, but by vigorously shaking your hands, clenching your fists and flicking the fingers out, like you were flicking water at someone, you can keep the muscles and tendons fully stretched.
There's a specific treatment for this but difficult to describe on the computer.
rob