Namecards should be white… well, at least some parts of it, because it is more economical to write on as supposed to a dark colour.
Sometimes, your client may want to write some stuff related to you, additional information not present in your well designed namecard. Your namecard is a convenient place to “add-on” this information. With that in mind, yes a black namecard may look cool, a glossy finish might look sleek, but both just make writing anything impossible.
