Button text color changes when clicked

Within my email, I created buttons with white text which link to additional information. Once email is sent. When the button is clicked the button text turns dark purple. The original color is only restored when you go out of the email and open again. Is there a place in CC where you can select the color of the font when the button is clicked? Or set the button so the font color doesn't change color when clicked? Please advise. Thank you