Elaborate a bit on the color theory post. The most important aspect of getting the colours correct in a picture is setting the white balance. It is a term used in digital photography that relates to the cameras attempts to remove colour casts due to the colour of the light source. By setting the correct white balance in a picture the colours will be correct. One can set the white balance either when taking the picture or, if one is shooting in RAW mode, in a photo editing program like Adobe Photoshop.
Our eyes adjust naturally to the colour fluctuations in color temperature of everyday lighting conditions. We judge all colours relative to the color of the whitest white. When setting the white point we use colour temperature as the way to adjust. The colour temperature is given in the unit Kelvin and says how much we must heat up a black oven for it to glow like the color does. Kelvin starts at the absolute zero which is the coldest anything can be, the electrons stands still. It increases in the same ways as Celsius, i.e, 1 Celsius = 1 Kelvin.
It is beneficial to memorize the Kelvin scale for the most common lighting conditions:
One of the best way to get correct color is to use a gray card. Take a picture with the light directly to the gray card in the scene, and then take the picture without it. In Photoshop, or other similar photo editing software, one can select the gray card as the white point and then synchronize the white point for the two pictures. It will remove the color casts from the light and give a much better basis for minor color corrections later.