They are both ground corn and are similar, but they are not the same thing. Polenta is made from a different type of corn (flint corn) than grits (dent corn). The two types of corn have a different makeup but they’re not so different when compared. Grits are ground differently and result in a coarser (usually) and more irregular texture than polenta. Polenta will be more flaky, but this would be hard to tell with the naked eye. Both polenta and grits can be found in the classic state or "instant," meaning they have been par-cooked and take less time, but have less flavor. The color is not a very helpful guide, even though some say grits are white and polenta is yellow. Grits can certainly be yellow and polenta can be white as well! Finally, grits are slightly starchier and tend to have a little more “creaminess” when cooked.