The reason why learning color theory is so essential in photography.
Eliminating Just one color out of an image can really make the difference of an image being good or bad. You can see how it looses its POP here by just eliminating the red in her dress. One of the reason being that red is so important here is because red is the COMPLEMENTARY of green (the green in the grass). Complementary colors are pairs of colors that are of “opposite".
This image is also interesting because it has orange and blue which are also complementary. I believe that's why this image really gives the feeling that it does. When using complementary colors, it is visually more appealing to choose a dominant color and use its complementary color for accents. Using one color for the background and its complementary color to highlight important element. This will make a huge difference to your images. It makes a HUGE difference when a photographer understands this while doing color photography.
In visual experiences, harmony is something that is pleasing to the eye as well. It engages the viewer and it creates an inner sense of order, a balance in the visual experience. When something is not harmonious, it's either boring or chaotic. At one extreme is a visual experience that is so bland that the viewer is not engaged. The human brain will reject under-stimulating information. At the other extreme is a visual experience that is so overdone, so chaotic that the viewer can't stand to look at it. The human brain rejects what it can not organize, what it can not understand. The visual task requires that we present a logical structure. Color harmony delivers visual interest and a sense of order. Analogous colors are any three colors which are side by side on a 12 part color wheel, such as yellow-green, yellow, and yellow-orange. Usually one of the three colors predominates. These concept works with all visual arts equally.