When a digital camera leaves the factory, it is set in such a way that it captures the most detail possible. Unfortunately, this means it is set for very low contrast, low saturation and it will usually be too bright. There are reasons for this.
1. It is set too bright because the rule of thumb for capturing detail with a device that captures a positive image (slide film, Polaroid and digital cameras) is to shoot for the highlights and develop for the shadows. The opposite holds true for negative images. This means that, if it is set too bright, it exposes the image so that the zone 10 areas (whites and highlights) will reveal detail when the photo is darkened in editing.
2. The contrast is set low so that the detail in the dark and light areas will be visible, even though it isn't if you are looking at it with your eyes through the viewfinder. The dark and white areas will be too grey.
3. The saturation is set low because rich dark colors hide detail, like the texture in cloth.
In order to bring it back to what it looked like when you were seeing it in the viewfinder, you have to adjust at least these three things, and that's at minimum. If you don't, your colors will look washed out, the whole photo will look like you are looking at it through a film of milk and it will look horribly flat (two-dimensional). You really need those dark shadows and dark colors in order to achieve the illusion of three dimensions (contour and depth). Thus you adjust these things and find the best compromise between detail and depth. Only then will your photos look their best.