Giving a UI button a Color at Start

I'm trying to assign random colors o an array of UI buttons. I have an array of Colors and an array of buttons but once I get get down to AssignColor I can't say b.Color.

using UnityEngine; using UnityEngine.UI; using System.Collections;

public class match : MonoBehaviour {

 public Image[] images;
 public float time = 30.0f;
 public float _score;
 public GameObject pausePanel;
 public Color[] colors;
 public Button[] buttons;
 public ColorBlock theColor;

 // Use this for initialization
 void Start () {
     _score = 0.0f;
     colors = new Color[3];
     buttons = new Button[16];
     theColor = GetComponent<Button>().colors;
     colors [0] = Color.red;
     colors [1] = Color.blue;
     colors [3] = Color.green;
 
 }
 
 // Update is called once per frame
 void Update () {
     AssignColor ();
     time -= Time.deltaTime;
     
     if (time <= 0) {
         time = 0.0f;
     }

     if (time == 0 && _score == 0) {
         pausePanel.SetActive (true);
     }

 
 }

 void OnGUI()
 {
     GUI.Box (new Rect (10, 10, 30, 20), "" + time.ToString ("0"));
     GUI.Box (new Rect (85, 410, 30, 20), "" + _score.ToString ("0"));
 }

 void AssignColor()
 {
     int colornum = Random.Range (0, colors.Length);
     foreach (Button b in buttons) {

     }

 }

}