My favorite matte board is Red Clay (Brown) a warm brown with red tending toward violet when compared with other earth tones of brown. Some brown mattes work well, depending on what’s available. Most any brown will work with wood, stressed wood frames. My work is bright so I tend toward color in the matte boards. Barn or Patriot Red, Dark Red Violet, Azure Blue, Blue, Dk or slate Blue, Pumpkin or Golden Yellow, Soft Green, Lt Blue or Lt Grey for dusk, dawn, changing weather, darker grey, black, gold, copper, silver. I can make most any matte board work but don’t go toward beige and sand or neutral tones very often. But it all depends on the image and the client. Prints going out in groups, or companion pieces, often are asked to be same color or can be contrasting, again depending on the image and design.
My current sizes in matte boards are 11×14 and 9×12 standard sizes, plus 12×16, 16×20, 8×10; and the images vary within depending on the sizing, usually 9×12, 12×16, 11×14, 8×10, 6×8, 5×7.