Can I call a function on a behavior attached to a prefab from it's spawner object?

I am making a falling block game. The blocks can be red, orange, yellow, green, or blue. Besides just having different materials, each color has other properties I'll need to implement later.

I also want it to be possible for other objects to change the color of each individual instance of Box later on. I'm not sure if this is formed correctly, but I don't get any errors with this code:

 public class BoxProperties : MonoBehaviour {
 
     public Material RedMat;
     public Material OrangeMat;
     public Material YellowMat;
     public Material GreenMat;
     public Material BlueMat;
 
     public enum BoxType {        Red, Orange, Yellow, Green, Blue    }
 
 
     public BoxType myType;
 
     ////snipped Start() and Update()
 
     public void setType(BoxType newtype) {
 
         switch (newtype) {
             case BoxType.Red:
                 renderer.material = RedMat;
                 break;
             case BoxType.Orange:
                 renderer.material = OrangeMat;
                 break;
             case BoxType.Yellow:
                 renderer.material = YellowMat;
                 break;
             case BoxType.Green:
                 renderer.material = GreenMat;
                 break;
             case BoxType.Blue:
                 renderer.material = BlueMat;
                 break;
         }
 
         myType = newtype;
     }
 }

I made setType() public so other objects can use it to change the type of any given instance.

Additionally, I have a non-renderable cube that represents a spawn volume. I am able to get the Box instances to spawn at random points in the cube and fall, but I am not sure how I can get at the prefab instance's setType method to set the type of box after spawning.

 public class SpawnBoxes : MonoBehaviour {
     private Vector3 nextpos;    //Randomly picked new spawn position
     private float collecttime;    //Counts how long has passed since the last spawn
     private GameObject nextbox;
 
     public float spawntime;
     public GameObject spawnee;    //Box object goes here
 
     // Use this for initialization
     void Start () {
         collecttime = 0;
     }
     
     // Update is called once per frame
     void Update () {
         collecttime += Time.deltaTime;
 
         if (collecttime > spawntime) {
             nextpos = randPos(renderer.bounds.size, transform.position);
             collecttime = 0;
             nextbox = Instantiate(spawnee,nextpos,Random.rotation) as GameObject;
             //Set type of nextbox, not sure how to access that function, but it's part of a component script attached to the Box prefab
             nextbox.GetComponent("BoxProperties").setType(BoxType.Green); //Doesn't work.
         }
     }
 //snipped randPos()
 
 }

I realize there are some other approaches, like making separate prefabs for each Box type and spawning one randomly, but I wonder if there is a way to make this call work?