Added extra property for moving cell.

I found out that the background of moving cell is completely dark if the cell background set to `clearColor`.

![before](https://cloud.githubusercontent.com/assets/797182/4008022/2a5f2670-29d0-11e4-857c-a7a88dd7cc69.gif)

So I add a property to it.

![after](https://cloud.githubusercontent.com/assets/797182/4008030/585805f6-29d0-11e4-914a-11c2a9b979ad.gif)