change button font color framemarket and marketpress

Gridmarket theme with marketpress installed. when a user has multiple variations the choose option button (to place an item in the cart uses a grey font. I want to change it to white.
This is the css using firebug.

http://mysite.com/marketpress/marketpress-includes/themes/icons.css?ver=2.7

/* Line 66 */

a.mp_link_addcart, a.mp_link_buynow

{

float: right;

font-family: "Helvetica Neue",Arial,Helvetica,"Nimbus Sans L",sans-serif;

font-weight: bold;

padding-top: 5px;

padding-right: 5px;

padding-bottom: 5px;

padding-left: 5px;

so I added color:ffffff to the icon.css
so that it looked like this but the text color didn't change. What am I doing wrong?

a.mp_link_addcart, a.mp_link_buynow

{

float: right;
color: #ffffff;

font-family: "Helvetica Neue",Arial,Helvetica,"Nimbus Sans L",sans-serif;

font-weight: bold;

padding-top: 5px;

padding-right: 5px;

padding-bottom: 5px;

padding-left: 5px;