Using Case function to determine the color of a field

What type of field is "Days Till Due"?

It is a numeric calculation 

Just a little syntax error.  
Case([Field],
evaluation, answer is true,
evaluation, answer if true, 
answer if non-else)

Try this:

Case([Days Till Due],
-3, "<div style=\"color:black; background-color:Red;\">&[Days Till Due]&</div>",
-2, "<div style=\"background-color:Yellow;\">&[Days Till Due]&</div>",
-1, "<div style=\"background-color:Yellow;\">&[Days Till Due]&</div>", "")

It partially worked in that the color did appear correctly when the due date was -1, I would like it so anything -3 or less would appear in red. So the -5 seen in the picture would appear in red, also with the numbers showing

Try this:

if(  [Days Till Due] <= -3, "<div style=\"color:black; background-color:Red;\">"&[Days Till Due]&"</div>",   [Days Till Due] >= -2 and [Days Till Due] < 0,"<div style=\"background-color:Yellow;\">"&[Days Till Due]&"</div>",  "")

This worked! Thank you!