In Excel 2010, how can I extend a formula down (updating cell references) and avoid overwriting the background and fonts of the cells below it?

For example, if I have the following Excel spreadsheet

How could I extend the formula in `$B$1`

down through rows 2, 3, and 4 without changing their background color to light blue, and making sure that the reference to `A1`

in the formula gets updated to `A2`

, `A3`

and so on?