Red ≠ Blue, but Red is close to pink. How would you measure the difference between two colors? If you figure out a metric for color difference, you could train computers how to compare pictures.

You could use the Red-Green-Blue values from a digital picture like a 3D (Euclidian) way:

In March 2024 Tim Chartler (and friends) published Data Science Distance: When Close seems far. The article describes switching from Euclidean distance