Mesh is getting black on change - unity3d

Question

I have written a small code, which is mooving vertices down on mouse click. The problem is in that mesh on change is getting black (only in some places).
Here's the code
using System.Collections;
using System.Collections.Generic;
using UnityEngine;
public class MinerScript : MonoBehaviour
{
public MeshFilter filter;
public MeshCollider col;
public GameObject Player;
public float mineSpeed = 200;
Mesh mesh;
Vector3[] vertices;
void Update()
{
filter = transform.parent.GetComponent<PlayerGravity>().mesh;
mesh = filter.GetComponent<MeshFilter>().sharedMesh;
vertices = mesh.vertices;
Ray ray = new Ray(transform.position, transform.forward * 2);
if (Physics.Raycast(ray))
{
if (Input.GetMouseButton(1))
{
int index = Mathf.RoundToInt(ClosestIndexToPoint(ray));
vertices[index] += (-Player.transform.eulerAngles) * Time.deltaTime * mineSpeed;
mesh.vertices = vertices;
mesh.RecalculateBounds();
mesh.RecalculateNormals();
Color[] colors = new Color[mesh.vertices.Length];
colors[index] = Color.red;
mesh.SetColors(colors);
//col.sharedMesh = mesh;
}
}
}
public float ClosestIndexToPoint(Ray ray)
{
if (Physics.Raycast(ray, out RaycastHit hit))
{
Mesh m = hit.transform.GetComponent<MeshFilter>().sharedMesh;
col = hit.transform.GetComponent<MeshCollider>();
int[] tri = new int[3] {
m.triangles[hit.triangleIndex * 3 + 0],
m.triangles[hit.triangleIndex * 3 + 1],
m.triangles[hit.triangleIndex * 3 + 2],
};
float closestDistance = Vector3.Distance(m.vertices[tri[0]], hit.point);
int closestVertexIndex = tri[0];
for (int i = 0; i < tri.Length; i++)
{
float dist = Vector3.Distance(m.vertices[tri[i]], hit.point);
if (dist < closestDistance)
{
closestDistance = dist;
closestVertexIndex = tri[i];
}
}
return closestVertexIndex;
}
else
return -1;
}
I don't think the problem is in color, as i've tried to apply the teture on it.
About code:
It throws a ray, and if it hits any mesh, it is calling func "ClosestIndexToPoint". It returns value of type float. This function gets the triangle a ray hits, and then finds the closest vertecs to it. Then it just mooves it down (or the rotation of our Player object, cause a have a non - flat mesh).