changing material color through C# script

Hi, The question is pretty clear. I thought it was just renderer.material.color But somehow the color doesn't change. Here is what I've got:

I started with a puzzle, which contains several pieces (or in this case pipes). The start function of this puzzle is:

 // Use this for initialization
     void Start()
     {
         blocks = new GameObject[Size, Size, Size];
 
         for (int x = -Size / 2; x < Size / 2; ++x)
         {
             for (int y = -Size / 2; y < Size / 2; ++y)
             {
                 for (int z = -Size / 2; z < Size / 2; ++z)
                 {
                     GameObject o = (GameObject)Instantiate(Block, new Vector3(x, y, z), Quaternion.identity);
                     Pipe p = (Pipe)o.GetComponent(typeof(Pipe));
                     p.PipeModel = PipeTypes[Random.Range(0, PipeTypes.Count)];
                     p.pipeColor = PipeColors[Random.Range(0, PipeColors.Count)];
 
                     o.transform.parent = this.gameObject.transform;
 
                     blocks[x + (Size/2), y + (Size/2), z + (Size/2)] = o;
                 }
             }
         }
 
     }

The pipe class looks like this:

 using UnityEngine;
 using System.Collections;
 using System.Collections.Generic;
 
 public class Pipe : MonoBehaviour {
 
     private PipeState state;
     private GameObject instance;
     private Color pipeColorHighlighted;
 
     public PipeState State
     {
         get { return state; }
         set
         {
             state = value;
             setStyle();
         }
     }
 
     private GameObject _pipeModel;
     public GameObject PipeModel
     {
         get { return _pipeModel; }
         set {
             _pipeModel = value;
             instance = (GameObject)Instantiate(_pipeModel);
             instance.transform.parent = this.transform.parent;
             instance.transform.position = this.transform.position;
         }
     }
     public Color blockColor = new Color(0.2F, 0.3F, 0.4F, 0.0F);
     public Color pipeColor;
 
     // Use this for initialization
     void Start () {
         pipeColorHighlighted = Color.red;  // default test color
         State = PipeState.Default;
     }
     
     // Update is called once per frame
     void Update () {
         // respond to clicking etc...
     }
 
     private void setStyle()
     {
         if (state == PipeState.Highlighted)
         {
             print(pipeColorHighlighted);
             instance.renderer.material.color = pipeColorHighlighted;
         }
         else
         {
             instance.renderer.material.color = pipeColor;
         }
         //instance.renderer.material.color = (state == PipeState.Highlighted) ? pipeColorHighlighted : pipeColor;
     }
 }
 
 public enum PipeState
 {
     Default,
     Highlighted,
     Hovered,
     Selected
 }

So far everything looks right. The pipes all get their correct color. But than, when I want several pipes to be hightlighted, I use this function:

 private void setHighlighted() 
     {
         for (int i = 0; i < puzzle.Size; ++i)
             for (int j = 0; j < puzzle.Size; ++j)
                 for (int k = 0; k < puzzle.Size; ++k)
                     puzzle.getBlock(i, j, index).State = k == index ? PipeState.Highlighted : PipeState.Default;
     }

But somehow this doesn't change anything. The colors just stay the same. I gues the problem is somewhere in the instantiation of the pipe objects. But I can't really find it.

Thanks for the help