I have a serious problem right here every time I write or copy a c# code I keep getting errors everywhere it says not supported in unity engine.

Questions & Answers
1

using UnityEngine;
using System.Collections;

public class block_start : MonoBehaviour {

void OnMouseDown () {
	Debug.Log{"Got a mouse click\"};
		renderer.material.color = Color.blue;
	}

	void OnMouseUp() {
		Debug.Log ("mouse is up\");
			renderer.Material.Color = Color.white	
	}

}
2

using UnityEngine;
using System.Collections;

public class block_start : MonoBehaviour 
{

 void OnMouseDown ()
 {
        Debug.Log("Got a mouse click");
        gameObject.GetComponent<Renderer>().material.color = Color.blue;
     }
     void OnMouseUp() 
   {
         Debug.Log ("mouse is up");
          gameObject.GetComponent<Renderer>().Material.Color = Color.white    
     }
 }
3

You have material with a M, needs to be lower case. Material is a class, same with Color.

renderer.material.color = Color.white;