Automatic Cell Highlighting

I am logging man hours for construction jobs. I have three columns that perform this function. One column for "Budgeted Hours", one for "Actual Hours" and one for "Remaining Hours". I input hours into the "Actual Hours" column daily and it updates the "Remaining Hours" column automatically. I want to set up a formula that will turn the "Remaining Hours" cell red if the number goes into the negatives. This will help provide a more noticeable alert for when we go beyond the number of hours we budgeted for the job verses how many we actually work.