How to determine the color of a neighboring point?

Question

Shaders

Good day everyone!
Introductory unity3d. shader.
there is a mesh with a bunch of submesh.
Each submesh has a color and let's say there is no texture.
How to determine that the color of the current point and one of the neighboring points is different?
Or how to determine that a neighboring point belongs to another submesh.
Or another way to determine that this point is a boundary point in a submesh.

Answer 1

Collider - did not help?
If it's not dynamic, immediately calculate the entire mesh in matrix format.
Mesh.GetIndices(int submesh)
Mesh.GetTriangles(int submesh)