Is the Acer/Japanese Maple grafted?

If they get less than 40% sun intensity--too thick a shade tree, too heavy a shade screen, too closely spaced a lath, or the wrong exposure under a porch or patio roof--they will be red at emergence, but will turn green with reddish veins soon after. I it is a case of some branches having red leaves,and some having green leaves, I would suspect shoots from the rootstock, as Kildermorie suggests.