InstantiateManager.cs

using UnityEngine;

public class InstantiateManager : MonoBehaviour
{

    [SerializeField]
    private GameObject _cube;

    private int _frameCount;

    enum ColorStatus { red, blue, green };

    ColorStatus _status;

    void Start()
    {
        _frameCount = 0;
        _status = ColorStatus.red;
    }

    void Update()
    {
        _frameCount++;
        if (_frameCount >= 60)
        {
            _frameCount = 0;
            var go = Instantiate(_cube);
            switch (_status)
            {
                case ColorStatus.red:
                    go.GetComponent<Renderer>().material.color = Color.red;
                    _status = ColorStatus.blue;
                    break;
                case ColorStatus.blue:
                    go.GetComponent<Renderer>().material.color = Color.blue;
                    _status = ColorStatus.green;
                    break;
                case ColorStatus.green:
                    go.GetComponent<Renderer>().material.color = Color.green;
                    _status = ColorStatus.red;
                    break;
            }
        }
    }
}