Unity Terrain - Tint TerrainLayers. Gets TerrainLayers assets used on selected terrain and applies tint/color.

TerrainColorTint.cs

using System.Collections.Generic;
using UnityEngine;

// https://gist.github.com/st4rdog/40fc14a8a256c2376ba121bca33d7571
// Gets TerrainLayers assets used on selected terrain and applies tint/color.
// TerrainLayer color can be changed in Debug inspector view.
public class TerrainColorTint : MonoBehaviour
{
	public List<Terrain> Terrains = new();
	public List<Color> TargetColors = new();

	void OnValidate()
	{
		if (Terrains == null || Terrains.Count == 0) return;

		var layersCount = Terrains[0].terrainData.terrainLayers.Length;

		// Init with current colours
		{
			if (TargetColors.Count != layersCount)
			{
				TargetColors.Clear();

				for (int i = 0; i < layersCount; i++)
				{
					TargetColors.Add(Terrains[0].terrainData.terrainLayers[i].diffuseRemapMax);
				}
			}
		}

		// Apply
		{
			for (int i = 0; i < Terrains.Count; i++)
			{
				var terrain = Terrains[i];
				if (terrain == null) return;

				for (int j = 0; j < layersCount; j++)
				{
					terrain.terrainData.terrainLayers[j].diffuseRemapMax = TargetColors[j];
				}
			}
		}
	}
}