When two conditions are better than one
When setting up conditional formatting for a cell, you're not limited to a single condition. You can set up several conditions, each with its own unique attributes that are used when its particular condition is true. Most of the time, you find that two conditions are completely adequate to cover all the possible contingencies.
To set up a second condition in the Conditional Formatting dialog box (Format → Conditional Formatting), you click the Add button after defining the first condition and the formatting to use when this condition is true. Clicking this button expands the Conditional Formatting dialog box by adding a Condition 2 area with identical controls for defining the second condition and the formatting that it applies.