Relay Flip

Relay Flip is interesting and simple. But it is not easy.
The rectangle board have some disordered black and white blocks. The surrounded grey blocks is the transition area. The board is divided into some subregion. Just draw a stroke on the blocks of each subregion. The black and white of the blocks where the line passed are reversed. For the subregion, the color of each row should be the same. The end of the line is next to the start of the next subregion. Finally the color of rows corresponding in all subregion must be the same.
Feature:
1. The size of board from 4*3 to 6*7.
2. The number of subregion from 1 to 4.
3. Concise interface and design.

Rules:

A. The whole board include disordered black and white blocks, and the gray block is the transition area.
B. The whole board is divided into several continuous sub areas.
C. Draw a continuous line in each sub area. The black and white of the block where the line passes is reversed.
D. The color of each row in the sub area should be the same. The end of the previous sub area is next to the start of the next sub area.
E. The color of the row corresponding to all sub areas is the same.