Returns the CIELAB chroma of the given color.

CIELAB chroma may give a better quantification of how vibrant a color is compared to HSV saturation.

\sa https://en.wikipedia.org/wiki/Colorfulness
\sa https://en.wikipedia.org/wiki/CIELAB_color_space

The source from which colors should be extracted from.
`source` can be one of the following:
* Item
* QImage
* QIcon
* Icon name

Note that an Item's color palette will only be extracted once unless you call `update()`, regardless of how the item hanges.

A list of colors and related information about then.

Each list item has the following properties:
* `color`: The color of the list item.
* `ratio`: How dominant the color is in the source image.
* `contrastingColor`: The color from the source image that's closest to the inverse of `color`.

The list is sorted by `ratio`; the first element is the most dominant color in the source image and the last element is the least dominant color of the image.

\note K-means clustering is used to extract these colors; see https://en.wikipedia.org/wiki/K-means_clustering.

The average color of the source image.

The dominant color of the source image.

The dominant color of the image is the color of the largest cluster in the image.
\sa https://en.wikipedia.org/wiki/K-means_clustering

The color closest to the inverse of the dominant color found in the source image.

An accent color extracted from the source image.

The accent color is the color cluster with the highest CIELAB chroma in the source image.

\sa https://en.wikipedia.org/wiki/Colorfulness#Chroma

A color suitable for rendering text and other foreground over the source image.

On dark items, this will be the color closest to white in the image if it's light enough, or a bright gray otherwise.
On light items, this will be the color closest to black in the image if it's dark enough, or a dark gray otherwise.

A color suitable for rendering a background behind the source image.

On dark items, this will be the color closest to black in the image if it's dark enough, or a dark gray otherwise.
On light items, this will be the color closest to white in the image if it's light enough, or a bright gray otherwise.

The lightest color of the source image.

The darkest color of the source image.