I use Westminster buffered mat board from Light Impressions. It is not white but very close to white. It is 4 ply. I cut the matts a little higher that in the middle of the board. I don't print larger than 11x14 and mat every thing from that size smaller on to 16x20. I use to not dry mount but have decided that it is much safer for the photograph to be dry mounted.
Every good professional gallery I have ever been in to see a show has had that off white color of mat. Definitely not black. That may be good in the commercial world but not in the art world.