GUIGameCountDown.cs

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

public class GUIGameCountDown : MonoBehaviour
{
    public Sprite[] CountDownSprites;
    public Color[] SpriteColors;

    static GUIGameCountDown _instance;
    static int _tickAnimParam = Animator.StringToHash("Tick");
    Animator _animator;
    Image _image;

    void Awake()
    {
        _instance = this;
        _animator = GetComponentInChildren<Animator>();
        _image = GetComponentInChildren<Image>();
    }

    public static void Display(int num)
    {
        int clampedNum = Mathf.Clamp(num, 0, 3);

        _instance._image.color = _instance.SpriteColors[clampedNum];
        _instance._image.sprite = _instance.CountDownSprites[clampedNum];
        _instance._image.SetNativeSize();
        _instance._animator.SetTrigger(_tickAnimParam);
    }
}