flashRoutine

public class DamageFlash : MonoBehaviour
    {
        #region Exposed_Variables

        [ColorUsage(true, true)][SerializeField] private Color flashColor = Color.white;
        [SerializeField] private float flashTime = 0.25f;
        [SerializeField] private SpriteRenderer[] spriteRenderersToFlash;
        [SerializeField] private AnimationCurve flashCurve = null;

        [Header("Material References")]
        [SerializeField] private string colorRef = "_FlashColor";
        [SerializeField] private string flashAmountRef = "_FlashAmount";

        #endregion

        #region Private_Variables

        private Material[] _materialsToFlash;

        #endregion

        #region Public_Variables

        #endregion

        #region Unity_Calls

        private void Awake()
        {
            _materialsToFlash = new Material[spriteRenderersToFlash.Length];
            for (int i = 0; i < _materialsToFlash.Length; i++)
            {
                _materialsToFlash[i] = spriteRenderersToFlash[i].material;
            }
        }

        #endregion

        #region Private_Methods

        private IEnumerator FlashRoutine(Action callback = null)
        {
            SetFlashColor();

            var currentFlashAmount = 0f;
            var elapsedTime = 0f;

            while (elapsedTime < flashTime)
            {
                elapsedTime += Time.deltaTime;

                currentFlashAmount = Mathf.Lerp(1f, flashCurve.Evaluate(elapsedTime), (elapsedTime / flashTime));
                SetFlashAmount(currentFlashAmount);

                yield return null;
            }

            callback?.Invoke();
        }

        private void SetFlashColor()
        {
            foreach (var material in _materialsToFlash)
            {
                material.SetColor(colorRef, flashColor);
            }
        }

        private void SetFlashAmount(float currentFlashAmount)
        {
            foreach (var material in _materialsToFlash)
            {
                material.SetFloat(flashAmountRef, currentFlashAmount);
            }
        }

        #endregion

        #region Public_Methods

        public void Flash(Action callback = null)
        {
            StartCoroutine(FlashRoutine(callback));
        }

        #endregion

    }