Change color of one cell based on another cell

Hi,
I am trying to create a speadsheet based on customer sales. In one cell it has "yes" or "no" to inform me on whether or not the customer is committed. In the cell Next to it is the # of days I have until this product is built. This cell counts down, and when it gets to a certain number it turns yellow and then red. But, I don't want the number of days cell to change color if it is committed(Yes) already. How do I do this? Thank you in advance!