Let's talk about what color space you should use for your picture. This question you have no doubt asked yourself at this point. The color space you use depends on what the final output of your images is going to be. If you take pictures, download them straight to your computer, and typically only view them on your monitor or upload them for viewing on the Web, then sRGB is fine. The sRBG color space is also useful when printing directly from the camera or memory card with no post-processing.
If you are going to have your photos printed professionally or you intend to do a bit of post-processing to your images, using the Adobe RGB color space is recommended. This allows you to have subtler control over the colors than is possible using a narrower color space like sRGB. To make your picture more suitable for printing first you have to tune your white balance on the camera.
If you find that your white balance just isn't quite right, it is likely due to the fact that the camera is using generic settings that are made to cover a specific situation, such as direct sunlight or shade. The problem is that even direct sunlight has a different color temperature depending on atmospheric conditions - how high it is in the sky, etc. This is also true for fluorescent lamps and incandescent light bulbs. As these bulbs get older the colors shift a bit, so the white balance setting doesn't exactly match.
For this reason to DSLR cameras was added a feature that allows you to fine tune the pre-existing white balance settings. This feature is accessed by entering the White balance menu in the Shooting menu. Once you have selected a white balance setting a small colored grid appears. This grid allows you to add up to 6 points of green or magenta and amber or blue to the current white balance setting.
Using the multiselector up adds green, down adds magenta, left adds blue, and right adds amber. Because green and magenta are opposite colors you can only add one at a time, the same with blue and amber. But you can add two colors together, as long as they aren't opposites. For example, you can add 4 points of green and 3 points of blue, which adds a blue-green tint to the existing WB setting. On the opposite side, you can add 4 points of magenta and 3 points of amber, adding a reddish-purple tint to the WB setting.
All in all it's actually more complicated to explain than it is to do. The grid gives you a pretty good idea of the color that you can add to the WB setting.