Grade A maple syrup typically has a milder flavor than Grade B, which is very dark.
The classification of maple syrup in the US depends ultimately on its translucence. US Grade A Light Amber has to be more than 75 percent translucent, US Grade A Medium Amber has to be 60.5 to 74.9 percent translucent, US Grade A Dark Amber has to be 44.0 to 60.4 percent translucent.
US Grade B is any product less than 44.0 percent translucent. Grade B is very dark, with a rich maple flavour. The dark grades of syrup are used primarily for cooking and baking, although some specialty dark syrups are produced for table use.