In photography and graphics, colour saturation is used to describe the intensity of colour in the image. A saturated image has overly bright colours. Using an image editing software like photoshop, one can increase or decrease the saturation. One can also increase the saturation by slightly underexposing the images or by using a Polarizing filter. The saturation can be reduced by over exposing on the other hand.
Some colours are inherently saturated to begin with. Typically the Red of a post office would be rendered quite saturated if its well exposed. Caution may be used while increasing the saturation of colours. If over done, they start to bleed and may not often look too good. Usually a small increment is good enough and that too if the colours form an integral part of the composition.