What Is Invisible Text?
Because search engines easily detect regular keyword stuffing, some spammers have supplanted regular keyword stuffing with the more subtle technique of using invisible text — also known as invisible keyword stuffing. Invisible text is the method of inserting hidden text — generally, keywords galore — into the body of a Web page by making the text the same color as the page's background, rendering the text invisible to the user, unless he/she highlights the text.
Like traditional keyword stuffing, invisible keyword stuffing is banned by most search engines, and because the latest incarnations of search engines are highly adept at detecting even invisible text, excessive use of this technique could lead to the removal of a Web site from Internet search engines' indices.
Thus, albeit less obvious than regular keyword stuffing, invisible text is still perceived as spamming and the technique therefore is not recommended as a means to improve search engine rankings. To avoid problems, make sure not to include any text whose color exactly matches the Web page's background color. In other words, if the page background is white, use a text color that is at least a slightly different hue than the background.