Gley Traffic System vehicle material randomizer, add this to your Vehicles to randomize materials when they are activated

VehicleColorRandomizer.cs

/*
 * Licensed under the MIT license
 *
 * MIT License
 * Copyright (c) 2025 Mike Wuetherick
 * 
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */
using System.Collections.Generic;
using Gley.TrafficSystem;
using UnityEngine;

namespace PixelWizards.Gameplay.TrafficSystem
{
    /// <summary>
    /// Listens to when a vehicle is activated and if it is
    /// this vehicle then randomizes the material for
    /// the specified mesh renderer.
    /// Add this to the same game object as the VehicleComponent
    /// </summary>
    public class VehicleColorRandomizer : MonoBehaviour
    {
        [Header("Which mesh are we applying the random material to?")]
        [SerializeField] private MeshRenderer colorMeshRenderer;

        [Header("List of materials to randomize")]
        [SerializeField]
        private List<Material> materials = new();
        
        private VehicleComponent thisVehicle;
        
        private void Awake()
        {
            Events.OnVehicleActivated += VehicleActivatedHandler;
            thisVehicle = gameObject.GetComponent<VehicleComponent>();
        }

        private void VehicleActivatedHandler(int vehicleIndex, int waypointIndex)
        {
            var vehicle = API.GetVehicleComponent(vehicleIndex);
            if (thisVehicle != vehicle)
            {
                return;
            }
            
            RandomizeMaterial();
        }

        [ContextMenu("Randomize Material")]
        private void RandomizeMaterial()
        {
            // randomize materials
            var randomMat = materials[Random.Range(0, materials.Count)];
            if (colorMeshRenderer)
            {
                colorMeshRenderer.sharedMaterial = randomMat;    
            }
        }
    }
}

Updated, this is under MIT license