|I like to sew summer shirts for DH, but he's very particular about buttons. Sometimes the only ones I can find to match the fabric are too shiny or not quite the right color. I've found that turning buttons over to their wrong side (which is generally the flattest side) and sanding with a bit of fine sandpaper or emery board makes them perfect for DH's shirts. Even the color changes slightly once the shine is gone. This has worked beautifully for the last 2 shirts I've sewn.
The buttons for the shirt I'm working on now aren't shiny, but I will turn them over so their flat side faces up because they just look better that way.
So consider that when it comes to buttons, there is no right or wrong side just the side that looks best.