Are you aware of the penalties for using hidden text? This out dated technique is Spam. Never try to add keywords or text to a page, in the same color font as the exact background color, thus making text appear hidden.
Spam Alert: Don’t EVER use hidden text, hidden links or hidden “anything” on a page unless you want to risk setting off some warning flags and risk getting in trouble.
Special Tip: Be sure to use care with text color inside of a table too.
Example: If your background is a white page and you are using a table filled with dark Navy Blue (for example.) Be careful not to use a white colored font text. Although the text is not hidden, you could still accidentally set off some flags by using a white text with a white background (regardless of the fact that the table is blue.)