Add a 'Vibrance' slider

[simjnd]

Adding a 'vibrance' slider could be a great addition.

The difference between vibrance and saturation is that saturation will affect the intensity of every pixel in an image while vibrance is a more sophisticated control that affects the intensity of colors in an image, but with more emphasis on preserving skin tones and other colors that are harder to adjust with saturation. Vibrance also works to reduce the saturation of already-saturated colors, thus making it easier to adjust the overall saturation of an image without over-saturating some colors.

Here is a side-by-side comparison: