Setter for **self.__colors** attribute.

        :param value: Attribute value.
        :type value: tuple

def colors(self, value):
        """
        Setter for **self.__colors** attribute.

        :param value: Attribute value.
        :type value: tuple
        """
        if value is not None:
            assert type(value) is tuple, "'{0}' attribute: '{1}' type is not 'tuple'!".format("colors", value)
            assert len(value) == 2, "'{0}' attribute: '{1}' length should be '2'!".format("colors", value)
            for index in range(len(value)):
                assert type(
                    value[index]) is QColor, "'{0}' attribute element '{1}': '{2}' type is not 'QColor'!".format(
                    "colors", index, value)
        self.__colors = value