Scott's got it.
The fact is - 98% of all galleries and museums want/use white matts. It's part tradition, but also largely - again, like Scott said - you dont want your matt to show up your print. When printing on warm paper, get a warm matt, cold toned paper, colder matt. You NEVER want your matt to be brighter than your highlights, b/c as your eye flows over the image, it's naturaly going to go tot the brightest spot... if it's the matt, the viewer is no longer looking at your image.

While black matts may look elegant, there should be a dam good reason for using them... it's just part of convention that they not be used. And, since they are hardly ever used, now, if you hang in black, everyone will be oogling your matts.. not the work. I dont recomend it when hanging in public.

Whether to matt - "full bleed" which shows the entire paper, to it's edge, and then gives a gap all around, or "over matted" which necessarily encroaches on the image a touch- is totaly a matter of taste.

Whatever you do with matt board, you want to make sure that it's not "wild", as no one wants to look at the matt. Keep it low key, in the "background"...