Color.Lerp 함수를 이용해 A 컬러에서 B컬러로 자연스럽게 변경하기

 float duration = 5; // This will be your time in seconds.
 float smoothness = 0.02f; // This will determine the smoothness of the lerp. Smaller values are smoother. Really it's the time between updates.
 Color currentColor = Color.white; // This is the state of the color in the current interpolation.
 
 void Start()
 {
     StartCoroutine("LerpColor");
 }
 
 IEnumerator LerpColor()
 {
     float progress = 0; //This float will serve as the 3rd parameter of the lerp function.
     float increment = smoothness/duration; //The amount of change to apply.
     while(progress < 1)
     {
        currentColor = Color.Lerp(Color.red, Color.blue, progress);
        progress += increment;
        yield return new WaitForSeconds(smoothness);
     }
     return true;
 }

출처

http://answers.unity3d.com/questions/328891/controlling-duration-of-colorlerp-in-seconds.html