The skin looks less "flat"/"clean" the face is more pale, the dark rings under the eyes are more noticeable, the lips are less red and the eyebrows are weaker.
However this is going to be extremely flawed, as it has to make assumptions about which parts of the face are made up and which aren't, probably exaggerating what it has to "correct" for. Also i wouldn't be surprised if this will struggle immensely with non white faces.
The photo on the left is with makeup; the photo on the right is without. On the leftmost image the lips are more saturated and have more defined edges and there is more shadow around the eyes.