A white marker requires a pigmented, rather than a dye base ink, to achieve the required opacity. With the ink technology available, we have been unable to manufacture a marker or pen that will uniformly lay down white ink. In the future, however, as new ink technology develops, it is quite possible we will be able to make a pigmented white ink marker. Until then we suggest trying Newell Brands white Sharpie Paint or Poster-Paint marker. It is a valve action marker, which requires a pumping action.