Formula + Conditional Formatting For No Of Days Before Due Date

Heres what I am trying to do:

I have a due date of 30/10/2007 in cell A2, I would like the cells in row 2 to change to the colour green 15 days before the due date (15/10/2007) and then I would like Row 2 to change to the colour Amber 10 days before the due date (20/10/2007).

This is what I was trying to do but it is not working for me:

____A_______________B__________C
1___Due Date________15__________10
2___30/10/2007______=a2-b1______=a2-c1

The Formula in B2 and C2 work fine.

I was then thinking that I could put a formula in Conditional formatting that says something like
If todays date is equal to b2 then Green else do nothing or If todays date is equal to c2 then Amber else do nothing

I can't figure out the formula for that though.