Generate the CSS representation of this RGB color.

        Returns:
            str, ``"rgb(...)"`` or ``"rgba(...)"``

def to_css(self):
        ''' Generate the CSS representation of this RGB color.

        Returns:
            str, ``"rgb(...)"`` or ``"rgba(...)"``

        '''
        if self.a == 1.0:
            return "rgb(%d, %d, %d)" % (self.r, self.g, self.b)
        else:
            return "rgba(%d, %d, %d, %s)" % (self.r, self.g, self.b, self.a)