Selective Coloring with a Perceptual Color Distance
Selective desaturation is an effect commonly used to highlight specific details or objects in an image.
Create a distance map between pixels of an image and a given color using ColorDistance with a perceptually accurate distance function such as the CIE2000 color difference.
Use the map as a mask to highlight the regions close to the target color.
Compose the original image and its grayscale version using the distance map.