Basic Color Theory
http://www.colormatters.com/color-and-design/basic-color-theory
I still think that the article's text "practices what it preaches", in terms of using color. Omitting the white and grey, the sub-heading and color examples use mostly a blue to purple range, exemplifying the first harmony example. To see the second, they use some green in the color examples, which stems across from purple. The article uses red some, which is still next to purple. They obviously did all of this on purpose.
Comment: Do you think that there are reasons not to use colors reflective of nature (unless you make a product based off of nature)?
I ask this because the article mentions some few ways to create color harmony. The reason I question nature is because the first two ways of creating harmony involve the color wheel. While the first two involve color theoretically, basing harmony off of nature is more practical, if you will. While all color harmonies are somewhat subjective, I feel that nature seems to more subjective in terms of visual "pleasure" (as the article defines it) than the science involved in the color wheel. However, this is basic theory, and I am unaware of other studies in color theory and the science behind harmonic colors in nature