Human skin naturally tends to be made up of different tones, but in some cases, variations in skin tone can distract from an otherwise pleasing portrait.
Your model might, for example, have done her makeup in a dark room, wearing boxing gloves, or in the case below where the model has beautiful skin, the skintone is ruined by greenish reflections cast from sunshine hitting grass in front of the model.
Traditionally, this was corrected in Photoshop using Frequency separation technique, or painting layers with "blend modes". Capture One has a dedicated tool for such situations and it's extremely quick and easy to use. Firstly, check out the green tinted areas around the models nose and mouth.
With Capture Ones Skin Tone tool, we use the selector tool to pick an example of the ideal skin tone from our models face. Then we can simply drag the hue uniformity slider to the right to shift tones towards this ideal. There are other tweaks you can make, but the hue uniformity slider is the most powerful and natural.
In the example below, at 100%, I've gone a bit overkill with it, just for the sake of illustration, but hopefully you can see how powerful this tool is in portrait photography, especially things like glamour, where there can be issues with skin tone around knees, hands, etc.
Of course, it is still a universal color tool, so it effects the whole image. As you can see, the outside of our models hat has shifted hue too. Luckily, this tool can also be applied selectively ("locally") using Capture Ones Layer/Mask tool. This feature has saved me HOURS of retouching time, in comparison to my older workflow.