HexGrid.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UI;

public class HexGrid : MonoBehaviour
{
    public int height = 6;
    public int width = 6;

    public HexCell cellPrefab;
    public Text cellLabelPrefab;

    public Color defaultColor = Color.white;
    public Color touchedColor = Color.magenta;

    HexCell[] cells;
    Canvas gridCanvas;
    HexMesh hexMesh;

    void Awake()
    {

        gridCanvas = GetComponentInChildren<Canvas>();
        hexMesh = GetComponentInChildren<HexMesh>();

        cells = new HexCell[height * width];
        
        for (int z = 0, i = 0; z < height; z++)
        {
            for (int x = 0; x < width; x++)
            {
                CreateCell(x, z, i++);
            }
        }
    }

    void Start()
    {
        hexMesh.Triangulate(cells);
    }

    void CreateCell(int x, int z, int i)
    {
        Vector3 position;

        // '/' rounds to the nearest integer, which is why this math works
        position.x = (x + (z * 0.5f - z / 2)) * (HexMetrics.innerRadius * 2f);

        position.y = 0f;
        position.z = z * (HexMetrics.outerRadius * 1.5f);

        HexCell cell = cells[i] = Instantiate<HexCell>(cellPrefab);
        cell.transform.SetParent(transform, false);
        cell.transform.localPosition = position;
        cell.coordinates = HexCoordinates.FromOffsetCoordinates(x, z);
        cell.color = defaultColor;

        Text label = Instantiate<Text>(cellLabelPrefab);
        label.rectTransform.SetParent(gridCanvas.transform, false);
        label.rectTransform.anchoredPosition = new Vector2(position.x, position.z);
        label.text = cell.coordinates.ToStringOnSeparateLines();
        label.text = x.ToString() + "\n" + z.ToString();
    }

    public void ColorCell(Vector3 position, Color color)
    {
        position = transform.InverseTransformPoint(position);
        HexCoordinates coordinates = HexCoordinates.FromPosition(position);
        Debug.Log("touched at " + coordinates.ToString());

        int index = coordinates.X + coordinates.Z * width + coordinates.Z / 2;
        HexCell cell = cells[index];
        cell.color = color;
        hexMesh.Triangulate(cells);

    }
}