Button color

Hello,
i have a problem with the color of button and wrritten color in the button:

http://www.dcgroupag.ch/index.php/kontakt

If u can see if u go with mouse over the button "Senden" the button become black, and the written in the button is black, how i can change the coloro of written and the color of button when u go over with mouse?

Thanks

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