Sometimes a realtor will ask why the photos don't match the colours of the room accurately. The reason is because our eyes and mind compensate for a huge variety of factors. It's able to take a lot of information and make it appear normal. Much like when you wear tinted sunglasses, at first you notice that colours are off but eventually your mind compensates and you stop noticing that they are coloured, everything looks "normal".
Much the same with rooms in a house, if you were to look objectively at a room and really analyze the colours you were seeing, you would usually start to see shifts and changes across a room that you normally wouldn't notice.
1) Ambient light or available light - is the light naturally found in a given room. Typically this would be coming from a window. Sunlight is perfectly neutral in colour but the light that comes streaming into a room could be reflecting off the grass, trees, water, walls of nearby buildings and thus comes in a variety of coloured shades.
2) Light sources - these include the overhead lights, lamps, potlights and flash units the photographer brings. Each of these light sources could be a different colour. Some might be greenish fluorescent, others a slightly warm yellow and some an almost orange tungsten. The flash unit a photographer uses will be of neutral hue but they can only compensate for one light source at a time.
3) The colours of the wall - any light hitting the walls of a room can bounce back and affect the general look of the room, especially in rooms with numerous walls with a reflective/shiny finish like wood paneling.
4) Time of day - sunrise and sunset lighting is much warmer then typical daytime lighting.
5) Weather - sunlight is neutral but cloudy skies can create a slightly cooler/bluer look to photos
What does this all mean? In any given room, their might be 4-5 different kinds of light. Standing in a living room you might have flourescent light from the kitchen streaming in, window light with a greenish cast flooding onto the floor, an entrance hallway with tungsten lights, all bouncing off wood panelled walls, in a neutrally lit living room with potlights. A photographer can try to compensate for one light source, but it's impossible to balance for all of them.
A photo will never look exactly like what your eye sees but we do our best to aim for an accurate approximation.