I saw a sample workbook which has data in the area of A1-G50, all cells
outside this area is grey-like. They are not really painted via grey
background color, nor could I repaint them as any other color. But I
can entered data into the cells. I tried to copy a cell from this
grey area to the data area, the value was copied but not the background
grey-like color.

How did they do it?