If you make any modifications to your theme at all, even changing a single color, you will want to create a child theme to prevent your changes from being overwritten when you upgrade your theme. This is a very simple process. All that is required to create a child theme is a directory with a single CSS file. And you can do more with a child theme than just change a few colors. If you make any changes to the functions.php file, you will want to add that file to your child theme as well.
More information and detailed instructions are available here in the WordPress Codex.