The first step to get pleasing color is to remove color casts and to balance the colors. For example, if you phograph a subject in shade, often the photo has a blue cast, while photos taken near sunrise or sunset have yellow/red casts. The warm color cast usually are pleasing, they are one of the peculiarities that make so beautiful the early morning or late evening light. Cold casts, instead, tend to detract from the photos.

To balance the colors, I use the Color Balance window (Image>Adjustments>Color Balance). This window has three sliders: Cyan/Red, Magenta/Green, Yellow/Blue. The sliders are complementary: for example, if you increase the Red component you automatically decrease Cyan. Check the "Preview" box and move the sliders to understand properly how they work: they are quite intuitive and after few tries you will be able to use them to achieve the desired results. For example, if the photo has a blue cast, you have to move the Cyan/Red slider towards "red", and the Yellow/Blue towards "yellow".

You can balance the colors separately into shadows, midtones and highlight. Usually, I do the main adjustment into midtones, then I adjust highlights and, if necessary, the shadows. If the photo has very light areas, you have to be careful with color balance: a strong adjustment might results in overexposed highlights. To get the best results, I recommend to leave unchecked the box "Preserve Luminosity".

The purpose of Color Balance is similar to the "White Balance" of the camera, but it gives much finer control on the image: this is one of the reason to use RAW file format and to fine-ture the colors with Photoshop. With Color Balance, you can either get very faithful colors, or give your preferred look to the colors. Personally, I like warm tones, so I often increase Yellow and Red a little more than what would be strictly necessary, to give a slight warm tone to the photo.

In some situations, the photo may had a very strong color cast that is difficult to remove - it does not happen often, but sometimes I've had to fight with strong cast that can't be easily removed with CB.

More often, I use the Replace Color (Image>Adsjustment>Replace Color) window. This window allows to select a color from the image and to replace it with another color; usually, it is better to select a replacement color quite similar to the original color, otherwise you get strong artefacts (noise and banding). The fist step is to select the color: with the color picker, click on the photo to select the color that you want to change. You can use the "Fuzziness" slider to select a narrower or a wider range of colors; the small preview under the slider shows the areas that you have selected (black means fully selected, white mean not selected, and the various shades of grey indicated different degrees of selection).

When you have choosen the color, you can choose the replacement. Click on the colored square into the Replacement box (above "Result") and select the replacement color. Be sure that the "Preview" box is selected, so you can check immediately the results; if you are not satisfied, you can try to change the degree of Fuzziness, or to set a lower value of Hue and Saturation, to reduce the difference between the original color and the replacement. I don't use always the Replace Color window, but it is useful when you want to change a specific color without affecting the other colors of the photo.

There are various other techniques to make selective color adjustments. If you want to change all the colors into a specific area of the image, the best way is to use the layer mask. Make a copy of the photo on a second layer and modify the colors with Color Balance or other tools until you get the desired results in the area that you want to change; don't worry if the rest of the photo doesn't have the right colors. Then, apply the Layer Mask "Hide All" to the copy and use a white brush to select the areas where you want to apply the effect. This technique is useful, for example, when you want to warm up the colors of the subject while leaving untouched the colors of the surroundings.

Another option, very simple but effective, is to use the Brush Tool. Create a new empty layer, that you can call "color enhancement with brush", and select the Brush Tool. Select a large and very soft brush (Hardness 0%), and set the opacity on a very low value (between 4% and 7%). Now, set the brush on the color that you want to enhance, and paint on the area that you want to improve. An example: you have photographer a nice Robin, but you are not satisfied by the colors, because the breast has a pale orange/yellowish color instead of a saturate orage/red. Set the paintbrush on red, and paint on the breast, with a brush sligtly larger than the area that you want to paint. Of course, you won't actually "paint" the image, since the opacity of the color is set on a very low value, but the brush enhances noticeably the tone. Select and desect the visibility of the "color enhancement with brush" layer to compare the photo after and before the effect: even with a very transparent brush, you can make a strong improvement. Remember that the color you add with the Brush subtracts information from the pixels of the subject; in other word, this techniques reduced the fine detail. If you set the opacity of the brush on 4-7% and you don't paint on the subject more than once, the loss of detail is truly negligible, but you don't have to exaggerate, otherwise you get an artificial-looking photo.

A useful tool to make selective saturation adjustments is the Sponge Tool. Sometimes I use this tool when I want to enhance the saturation into a specific area of the photo without using the layer mask. I recommend to use always soft brushes and to set the degree of the effect (the "Flow" box) on a value between 10% and 30%. While it is not one of the tool that I use often, it is useful to make small corrections when you have finished the main processings. You can also use this tool to reduce the saturation, if you notice that an area of the image has become oversaturated.