I think I would use a muted off white like an antique white, earth tones, or pastel color that you like. Stay away from any sort of pure white. I think the stark contrast between black framed black & white photos against a bright white background would be too stark. Also stay away from any sort of dark or bright colors. If the wall color disappears, and the focal point of the wall is the photos, it is perfect. If you are not sure what color to settle on, narrow it down to 2 or 3 colors and pick up a quart of each. Paint a 3 foot square section of wall and attach a picture to it to see what looks best. If you get it right, everyone will notice the photos and no one will remember what color the wall is.