Your formula is correct- the different colors are possible with
conditional formatting. Land the cell pointer on your formula cell and
on the menu click Format Conditional Formatting. You can then set
the parameters of your conditional format: if the cell value is between
one number and another number, shade the cell with a certain color.
You can click the Add button on that window to shade the cell with a
different color when the cell value is in another range. Your post
talked about a project aging at 30, 45, and 60 days- you'll need to
define the parameters of the conditional format according to the
definition of "30 days old" your company uses.