There are three main ways in which you can adjust colour, brightness, contrast, hue etc.
The Image Menu.
Under the Image Menu you will find the following:
Auto Tone - Tone refers to the degree of lightness or darkness of an area.
Auto Contrast - Contrast is the difference between the lights and the darks. If you have a picture that has little contrast, its usually very subdued. If you take an picture and turn down the contrast, the light parts of the pic become darker, and the dark parts become lighter.
Auto Colour - Removes colour casts. A colour cast is a tint of a particular colour, usually unwanted, which affects the whole of a photographic image evenly.
Certain types of light can cause film and digital cameras to have a colour cast. In general, the human eye does not notice the unnatural colour, because our eyes and brains adjust and compensate for different types of light in ways that cameras cannot.
If you click these the computer selects for you what it thinks are the optimal settings for each of these.
You can also adjust manually.
Image > Adjustments >
This allows you to adjust
Allows you to adjust the levels of each colour individually
Saturation is a uniform bumping up the intensity of all colors in your shot, regardless of the starting point of the colors. This can result in clipping (over saturation of certain colors which results in loss of detail in those areas) and over saturation of skin tones leaving them looking too orange and unnatural.
Vibrance is a smart-tool which cleverly increases the intensity of the more muted colors and leaves the already well-saturated colors alone. It’s sort of like fill light, but for colors. Vibrance also prevents skin tones from becoming overly saturated and unnatural.
Colour Balance and more.
These tools allow you to use your judgement to adjust a photo to look the best according to your own tastes.