Great care should be taken when choosing your mat board. Black may have a tendency to make your prints appear washed out or discolored. The dmax in your images may be toned and a black mat will bring out the toning in these areas a bit too much. An overly yellowish mat will definitely highlight selenium toning because yellow is the complimentary to violet, and as such will make your dmax seem overly purple. The best solution I find is to use cotton rag mat which is natural in color, that is to say, almost pure white and is archivally sound. Bainbridge makes this as well as Crescent. This particular board does not detract from your highlights and will present your image in a professional manner. There are quite a few venues that will only present fine art photography in white rag mats.