Hate to break it to you, but you're just used to bad makeup if you can see it clearly. You shouldn't be able to see foundation at all, if it matches her skin tone. All it should do is even out her skin tone, it shouldn't be any darker or lighter. And blush should look even less noticeable than Demi Lovato's natural blush in her makeup-less picture. She has a pretty serious natural blush.. almost too much for my taste. I'm just saying, you're assuming you can always tell when a woman is wearing makeup. And that's true if she's wearing bad makeup. But I guarantee you that you see women all the time in subtle makeup that suits them and you think they aren't wearing any.
How many men have you seen wearing makeup lately? None? Probably wrong. Men's makeup is seriously on the rise (yes, even with straight men), but it is meant to look like he's not wearing any. And it does. Women's makeup should be the same... but most women don't know enough about makeup to pull it off.
Example from the NYT website: