Conditional Formatting Based Upon Various Dates

I have a spreadsheet I'm trying to make which will have various cells change color based upon the date entered compared to today's date. Here are the details of it, and what I've tried to do so far:

Various safety tickets that employees acquire have a 3 year expiry date on them. What I want to do is be able to enter in the issue date, and then have the conditional formatting color the cell that contains the date based on the following criteria:

Green = More than 6 months remaining
Yellow = Between 6 months and 30 days remaining
Red = 30 days until expiry

Black = Expired (I wanted to eventually add this one, but Excel 2003 was only allowing me to add 3 conditional formatting conditions, so I just went with the 3 colors. I'm getting Excel 2007 later today, so I might be able to add more with that)

Now here is what I have so far:

3 years = 1095 days, 2.5 years = 913 days, 2 years and 11 months = 1065 days

N3 = 913
N4 = 1065

Conditional Formatting on cell C21

Condition 1 - color Green

=$C21+$N$3>=TODAY()

Condition 2 - color Red

=$C21+$N$4<TODAY()

Condition 3 - color Yellow

=AND($C21+$N$3<TODAY(),$C21+$N$4>TODAY())