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.