I completely agree that even with characters who have a "natural look," it's important to consider makeup. I've looked at some of my own pictures of costumes that I practically killed myself to make and realized that if I'd only worn just a little bit of makeup, it would have really looked perfect, but instead, my face looks flat and washed out. One of the most important things I try to remember, especially when tempted to go without makeup when cosplaying as an "au naturale" character or a male character is that we're dressing up as two-dimensional characters in three dimensions. When drawing anime, black pen on white paper, every detail on every character is drawn. If they left the area blank (as if we left our faces blank) the details would not be seen. And, especially with eyes, that's a very important point to remember. Take one of my boys, Miles Edgeworth. Edgeworth does not, has never and probably never will wear eyeliner or mascara. We know this. However! In any picture you might find of him, it's plain to see that his eyes are defined with black outlines, given the impression of long, dark lashes and downward-arched brows (as though he's frowning. Which he usually is.) Even though it tempts me to say "He's a man, he doesn't need makeup," the simple fact is that he may not, but I do. In addition to my usual moisturizer/primer/concealer/foundation/powder makeup, I always wear tons of mascara, narrow eyeliner just on the waterlines of my eyes (to keep the look "natural " even though it is not) and use deep gray powder on my eyebrows to match my haircolor (which is important as well, especially with unnatural colors!), in addition to plucking and styling them in such a way that they make that "knitted brow" shape. If I left my brows blond, they would completely disappear on my face, especially after applying my other eye makeup. I even apply some of my foundation lightly on my lips to cover their natural medium pink color, as such that he is drawn, his lips are as pale as the rest of his face. All this gives my face the definition Edgey's has naturally because he's a drawn character. I wouldn't wear blush with this character since I feel it would give the wrong look for what I'm after, but in many cases, I agree that it adds back much-needed definition to a fully made-up face, especially on most any female character (especially little girls).
Great tips, everyone; I've learned so much from all of you! ^.^