The human visual system automatically compensates for the color of light from various sources and it attempts to make the light white in color even when those sources are mixed. With camera sensors, each model has its own response to color that is relative to the ICC profile selected in Capture One's Base Characteristics panel and that varies under different lighting conditions. It is this response that results in a color cast in your images.
With RAW files, the color cast can be removed by neutralizing or "balancing” color values in Capture One. However, as white balance is interpreted in-camera at the time of capture, some care is required if you are capturing JPEGs. Although Capture One can apply some adjustments retrospectively to JPEGs using the camera's auto white balance setting, there is far less flexibility with previously processed files. In general, it is good practice to set an appropriate white balance setting or adopt an in-camera preset for JPEG’s based on your creative intent.
Alternatively, using a gray card or reference target for custom white balance settings, either at the time in-camera or retrospectively with Capture One, can simplify and even accelerate your workflow, helping you achieve accurate and consistent results with both RAW and JPEG files.
When it is necessary to adjust the white balance, Capture One has a dedicated tool that is flexible and easy to use. Like every other tool in Capture One, altering the white balance has no effect on your source files until you go to process them. Even then Capture One makes identical copies to create a new image file instead.
Capture One's White Balance tool is located within the Color tool tab and has several controls, including the Auto Adjust option, a number of presets, a picker (eyedropper), and two sliders which are meant to be used to fine-tune the results if necessary.
Four White Balance presets can be found under the Mode fly-out menu. These represent the most commonly encountered light sources (i.e., Daylight, Flash, Tungsten, and Fluorescent). Simply select the most appropriate, according to the scene. In addition, the Mode menu can display Custom and Shot options. The latter refers to the white balance used by the camera at the time the image was captured, while the former is displayed when the user makes a new white balance adjustment.
When accuracy is paramount, the picker (eyedropper) can be used on a gray card or reference chart. Alternatively, you can click on any white surface that is not clipped.
The Auto Adjust option is included in the tool title bar. Although it is useful for a quick adjustment, it should be considered as an initial step. As a result, it is not enabled as one of the default settings of the Auto Adjust option (available from the Adjustments menu or from the toolbar).
The Kelvin slider initially displays the color temperature selected by the camera and can be overridden within the range of 800 to 14000 degrees Kelvin. The scale on the slider represents the actual Kelvin value, which is subject to slight variations from camera to camera. Moving the slider to the right will achieve a warmer (yellow) look. Moving the slider to the left will result in a cooler (blue) appearance. This could be confusing, as the slider indicates the effect regarding what that slider does to the image, as opposed to the color temperature of the source of light. So, imagine that you have an image shot during sunny noon. The color temperature of the scene would be around 5500K. If you set the image's color temperature to something lower, then the image would become cooler/bluer, to counter the lower (hot/red) temperature of a light source.
The Tint slider also displays the setting selected by the camera to start with and can be fine-tuned to remove green and magenta tints. Both sliders are updated when new white balance adjustments are made.