Yup! When a horse sheds its winter coat (or summer coat, although primitive horses only shed in the spring) it sheds in some kind of pattern. One thing horsemen often notice is that patterned horses often shed the white hair first, then the colored hair, or vice versa. This can be very noticeable in some cases - but is completely normal.
So are bald patches - sometimes a horse will shed out an area a little bit prematurely, before the new coat has started to grow properly.