public override void update (float t)
{
CCRGBAProtocol tn = (CCRGBAProtocol) _target;
tn.color = new Color32 ((byte)Mathf.RoundToInt( _fromR + _deltaR * t),
(byte)Mathf.RoundToInt(_fromG + _deltaG * t),
(byte)Mathf.RoundToInt(_fromB + _deltaB * t), 1);
}