Unwanted color cast from incorrect white balance or mixed light sources — cold illumination overwhelming warm practical lights. Occurs when mixing daylight and tungsten without correction.
You know the scenario: You're on location, the sun is shining warmly into the room, and then you add interior lighting — suddenly everything appears tinged with green or blue. That's color contamination. Not just an aesthetic flaw, but a technical problem arising from the mix of light sources with different color temperatures. Your camera cannot be calibrated for both Daylight (approx. 5600K) and Tungsten (approx. 3200K) simultaneously. If you choose the wrong white balance, one light source will be corrected, while the other will exhibit a cast — either blue or yellow-orange.
In practice, this often happens unconsciously. You set the camera to Tungsten because the spotlights are the dominant light, and then daylight streams through the window — the external lighting immediately appears cold and artificial, while the window looks normal. Conversely, with white balance set to Daylight, your carefully placed 2K fixture looks orange and unnaturally warm. This isn't a material error, but pure camera logic. You have to decide: Which light source will be the reference?
Practical Solutions on Set: Either you filter one of the light sources — CTB (Color Temperature Blue) on the warm spotlights to match them to Daylight, or ND/CTO (Color Temperature Orange) on the window if you want to balance for Tungsten. Or you set the white balance to a neutral reference between the two. Some DoPs intentionally use color contamination as a stylistic device — for example, when a scene is meant to feel psychologically cold, and the cold external lighting expresses exactly that. But this is a conscious decision, not a mistake.
In the edit, color contamination can be partially corrected with color grading, but only if the sensor still has enough information — RAW material is more forgiving than H.264. The clean solution happens on set: correct white balance, harmonized light sources, or intentionally staged. A light meter reading with a ColorChecker is your best friend here, especially with mixed lighting.