I need the color of the cell to change when within 30 days of today's date

[splate]

I have looked and found many similar posts, but none of them seem to work.

I am working on a list for my wife; she has the names of foods in the refridgerator in column A, the quantities in column B, and the Expiration Dates in Column C. Row 1 is titles. What I am trying to do is format Column C to where it will turn green if the expiration date is within 30 days, yellow if it is within 15 days, red if it is within 5 days, and black when it has expired. I cannot get any of the formulas to line up; it seems as though random cells are highlighted. Please help?