$(this).find('option:selected').css("color") doesn‘t work in firefox 49.0.2

$(this).find('option:selected').css("color") doesn‘t work in firefox 49.0.2

when i use $(this).find('option:selected').css("color") to get the color of the selected option, it give me "rgb(255,255,255)" , not my real color. But when i try in on chrome , it works well.