You need to use two conditions

One is for the date in the cell to be less than now

i.e. the condition is less than = NOW()

with the pattern set to red.

Then press the add button and add a new condition

i.e. the condition is less than = NOW()-92

with the pattern set to amber.

92 = 3 month's worth of days.

Excel gives precendence to the first condition when both are satisfied.