From a local point of view one can take to be Euclidean space.

The distance between two points in Euclidean space is the length of a straight line from one point to the other.

Typical examples are the real numbers or any Euclidean space.

Another familiar example might be the compact 2-torus or Euclidean space under addition.

For Euclidean space, it is point reflection in the origin.

It may be embedded in Euclidean space of dimensions 4 and higher.

In three-dimensional Euclidean space there are 16 such normal forms.

Thus a humanly perceived color may be thought of as a point in 3-dimensional Euclidean space.

This is, in fact, a sharp contrast with the case of Euclidean spaces.

To describe such an orientation in 3-dimensional Euclidean space three parameters are required.