Use Conditional Formatting

Example: We have a series of test results that should all fall in the range of 1-5.  So we want any results above or below that range to be readily apparent.

1. Highlight the cells to be included in the conditional formatting.  Since these three columns of results are not a contiguous range, we'd hold down CTRL while highlighting each set of numbers.

2. Choose Format - Conditional Formatting.

3. For our first condition, we click the second drop-down arrow and select less than.  

4. Next, we'd type 1 in the third box, then click the Format button.

5. At Format Cells, we choose the Font tab.  Then we set the Font style to Bold Italic, and use the Color drop-down arrow to select red.  Click OK.

6. The Conditional Formatting box shows both our condition and format.  But since we also want to "flag" numbers larger than 5, we need to add another condition.  (You can set 3 conditions.)  So we click on Add.

7. Although 5.00 is technically within our acceptable result range, since it's right on the edge, we've decided to also flag that number.  So for Condition 2, we follow the same general process, but we set our condition to greater than or equal to and the number as 5.  We use the Format button and choose bold and green.  Then, click OK.

8. Our two types of conditional formatting are applied, and it's easy to spot which numbers are above or below our normal 1-5 range of test results.