How to change font color in Excel based on cell value?

I'm adding an answer here that combines the actual steps from the tutorial that @JNK supplied, and updates for Excel 2013/2016 that @JohnDyer supplied in his comment.

You never know when one of Microsoft's links just stops working.

+1 @JNK

+1 @JohnDyer

How to Apply Conditional Formatting

To apply conditional formatting to one or more cells:

1. Highlight your cell or range of cells.
2. Select the Conditional Formatting button on the Home tab of the ribbon.
3. Select Highlight Cell Rules.
4. Select a cell evaluator from the second drop-down box.
5. Enter your values in the dialog that pops up.
6. Click the OK button.

What you are looking for is conditional formatting.
Here's a quick tutorial.