At the outset, I will note that color rendition is definitely a matter of taste. Some people like warm colors and some like cool colors. Some like deeply saturated colors and some insist on "accurate" color rendition. This post isn't intended to say that any style is better than another, but simply to give a few pointers on how to get your photos to look more like you want them to look.
Digital cameras record images with values for red, green, and blue (RGB). Combinations of those three primary colors allow us to see other blended colors like yellow, brown and purple. Each pixel in a photo ends up specifying a value for each of the three primary colors. (It doesn't start out that way in the camera, but that's a different story.) In a jpeg file, the values for each color range from 0 to 255. For example, a particular pixel might be R200, G50, B 50. You can easily imagine that that pixel would be strongly reddish in color since the R value is high and the other values are much lower.
Note that the RGB values also specify brightness in addition to color. A pixel that is R255, G255, B255 is the brightest possible white; R0, G0, B0 is the darkest black; and R128, G128, B128 is medium gray. Colors with equal amounts of R, G and B are "neutral."
With that very simple background information, we can understand that the problem of getting good colors in our photos boils down to having the digital photo file specify the correct RGB numbers for the colors that we want to be represented in our photos. For example, suppose we are taking a photo of our friend who is wearing a white shirt. We know that the shirt is white (a neutral color), so the RGB values should probably be something like R225, G225, B225. Those values could be a little more or less depending on how bright the shirt should appear, and they could be a little bit to one side or the other of neutral if the shirt is not a pure white, but the three values should be basically equal and should be high enough to depict a bright white . Now imagine that we take the photo of our friend when he is standing on the north side of a tall building on a clear day, so he is in deep shade. His shirt will not be brightly lit and all the light falling on it will be blue light from the clear blue sky. Our camera will "see" the shirt as much darker than we would like it to appear in a photo and it will "see" the shirt as having a strong blue tint--maybe something like R140, G140, B200. Our friend's features will have the same problem--his skin will appear to have an unhealthy bluish tint and darker than normal coloration.
What is the solution??? Most people understand that the solution to the problem of having a photo appear too dark (or too bright) lies in adjusting the exposure. If you take a photo in the shadows, you must increase the exposure...letting in more light which will result in higher RGB values...so your photo will show the subject clearly. Most cameras are capable of setting the exposure automatically, and most of them do a more or less acceptable job of it most of the time.
But what about the problem of getting the colors right?? The solution to getting proper color in digital photos lies in the concept of white balance. Since we know that neutral colors must have equal parts of R, G, and B, we can correct the colors in a digital photo by mathematically adjusting the RGB values so that a pixel we know should be white (or other neutral color) will have equal parts R, G and B. Applying the same mathematical adjustment to all the pixels in a photo will bring all the other colors into line also.
Almost all digital cameras have one or more ways of setting the white balance so our photos look more like we think they should. Automatic white balance is the easiest and most common method of setting the white balance. Just like an automatic exposure setting, the camera tries to estimate the proper white balance based upon a reading of the particular scene using algorithms supplied by the camera manufacturer. Since the camera has no way of knowing whether it is looking at a white shirt or a red flag or whatever, it is amazing that automatic white balance works at all--it does work, but not always and not as well as we would like. Another way of setting white balance is by specifying the lighting conditions with a menu setting, usually in terms like "daylight," "cloudy," or "fluorescent." That method can work okay if the particular lighting conditions happen to match what the camera designer had in mind...but it won't work if your subject is standing in daylight next to a red barn that is reflecting red light back on her face because the daylight setting doesn't account for all that redness. A third way of setting white balance (available in more advanced cameras) is by shooting a reference shot of a known neutral subject (usually a special white or gray card available from photo stores). That will provide a very accurate white balance setting, provided the reference card can be positioned in the same location as the subject, which is not always possible if you are taking a photo looking into a shaded canyon from a viewpoint in the sunlight (or vice versa).
If you or your camera cannot set the proper white balance at the time you take a photo, then the only solution is to adjust the white balance (and other color settings) in "post processing" after the fact. Some cameras allow you to do limited editing or processing of the photos in the camera, but in most cases post processing is done by downloading the photo files to a computer or tablet and editing them with some sort of post processing software. That software can be something sophisticated like Adobe Photoshop or Lightroom, or it can be the free software that often accompanies new cameras, or it can be some of the various free or inexpensive software available online.
If you want to do post processing of your photos, it is highly recommended that you shoot your photos in RAW format. In the simplest terms, a RAW file preserves the digital information captured by the camera without any alteration. In particular, the RAW information is preserved without any white balance adjustment having been applied. That means you are free to apply any white balance adjustment you think is required to get the correct color appearance. If you have a jpeg file which has already had a white balance adjustment applied by the camera, you can generally apply a further adjustment to try to get the colors looking right but it is a bit like trying to paint over a mistake--it is far better to get it right the first time.
Here is a simple example of color correction. The photo below was shot and corrected in RAW format but of course the photos displayed here are jpegs since that is the typical way to show photos online. The corrections were done using Adobe Lightroom software but the same adjustments could easily have been done using the free RAW conversion software from Canon that came with the camera and the method of making the adjustments would have been almost the same.
Here is a photo of Wahclella Falls. It was deliberately underexposed so that the water in the falls did not end up overexposed--that resulted in the rest of the photo being very dark. The white balance was set on automatic. The camera recognized that the light was very green because of all the trees in the area and so the camera applied a strong magenta adjustment to correct for the green tint. But the camera did not recognize how blue the light was, so the overall color tone of the photo is very cool. If I had set the white balance to something like a "shade" setting, the photo would have been warmer, but then it would have been too green because the "shade" setting doesn't contemplate all the green tint from vegetation.
To correct the color balance, I used the white balance tool in Lightroom. Most photo editing programs have something like that tool--generally you click on a button that looks like a little eyedropper. Your cursor then changes to an eyedropper and you simply click it on an area in the photo that you want to have a neutral color. In this case, I clicked on the water in the falls to make it a pure white. I could also have clicked on some rock that I believe should be a neutral gray or anything else that should be neutral. Sometimes you have to click multiple times to find a good adjustment, and failing that, you have to move the white balance sliders in the program. Usually there is a slider that goes from warm to cool and a slider that adjusts the tint from green to magenta.
After correcting the color, I simply adjusted the brightness and contrast with sliders to correct for the intentional under-exposure, and then moved the saturation slider a little bit to give the colors some more "pop." Specifically, I increased the exposure slider (brightness) by a little more than one stop, decreased the highlights slider so that the water didn't appear over-exposed, and increased the contrast slider until the appearance looked about right.
Obviously, many more adjustments are possible depending on what you want to accomplish. But the simple color adjustment accomplished by locating a neutral color in the image and clicking on it with the white balance tool, combined with adjusting the brightness and contrast, gives you a great start on the image. Those who like warmer colors can simply slide the color balance adjustment a bit more to the warm side. Those who like deeply saturated colors can push the saturation slider.
