Unity3d Color Picker

ColorPicker.cs

using UnityEngine;
using System.Collections;

// relies on: http://forum.unity3d.com/threads/12031-create-random-colors?p=84625&viewfull=1#post84625

public class ColorPicker : MonoBehaviour {
  
  public bool useDefinedPosition = false;
  public int positionLeft = 0;
  public int positionTop  = 0;
  
  // the solid texture which everything is compared against
	public Texture2D colorPicker;
	
	// the picker being displayed
	private Texture2D displayPicker;
	
	// the color that has been chosen
	public Color setColor;
	private Color lastSetColor;
	
	public bool useDefinedSize = false;
	public int textureWidth  = 360;
	public int textureHeight = 120;
	
	private float saturationSlider = 0.0F;
	private Texture2D saturationTexture;
	
	private Texture2D styleTexture;
	
	public bool showPicker = false;
	
	void Awake() {
	  if (!useDefinedPosition) {
	    positionLeft = (Screen.width / 2) - (textureWidth / 2);
	    positionTop  = (Screen.height / 2) - (textureHeight / 2);
	  }
	  
	  // if a default color picker texture hasn't been assigned, make one dynamically
	  if (!colorPicker) {
	    colorPicker = new Texture2D(textureWidth, textureHeight, TextureFormat.ARGB32, false);
	    ColorHSV hsvColor;
  	  for (int i = 0; i < textureWidth; i++) {
  	    for (int j = 0; j < textureHeight; j++) {
  	      hsvColor = new ColorHSV((float)i, (1.0f / j) * textureHeight, 1.0f);
          colorPicker.SetPixel(i, j, hsvColor.ToColor());
        }
  	  }
	  }
	  colorPicker.Apply();
	  displayPicker = colorPicker;
	  
	  if (!useDefinedSize) {
	    textureWidth = colorPicker.width;
	    textureHeight = colorPicker.height;
	  }
	  
	  float v = 0.0F;
	  float diff = 1.0f / textureHeight;
	  saturationTexture = new Texture2D(20, textureHeight);
	  for (int i = 0; i < saturationTexture.width; i++) {
	    for (int j = 0; j < saturationTexture.height; j++) {
        saturationTexture.SetPixel(i, j, new Color(v, v, v));
        v += diff;
  	  }
  	  v = 0.0F;
	  }
	  saturationTexture.Apply();
	  
	  // small color picker box texture
	  styleTexture = new Texture2D(1, 1);
	  styleTexture.SetPixel(0, 0, setColor);
	}

	void OnGUI(){
	  if (!showPicker) return;

	  GUI.Box(new Rect(positionLeft - 3, positionTop - 3, textureWidth + 60, textureHeight + 60), "");
	  
		if (GUI.RepeatButton(new Rect(positionLeft, positionTop, textureWidth, textureHeight), displayPicker)) {
  		int a = (int)Input.mousePosition.x;
  		int b = Screen.height - (int)Input.mousePosition.y;
		
  		setColor = displayPicker.GetPixel(a - positionLeft, -(b - positionTop));
  		lastSetColor = setColor;
		}
		
		saturationSlider = GUI.VerticalSlider(new Rect(positionLeft + textureWidth + 3, positionTop, 10, textureHeight), saturationSlider, 1, -1);
  	setColor = lastSetColor + new Color(saturationSlider, saturationSlider, saturationSlider);
		GUI.Box(new Rect(positionLeft + textureWidth + 20, positionTop, 20, textureHeight), saturationTexture);
		
		if (GUI.Button(new Rect(positionLeft + textureWidth - 60, positionTop + textureHeight + 10, 60, 25), "Apply")) {
		  setColor = styleTexture.GetPixel(0, 0);

  		// hide picker
  		showPicker = false;
		}
		
		// color display
		GUIStyle style = new GUIStyle();
		styleTexture.SetPixel(0, 0, setColor);
		styleTexture.Apply();
		
		style.normal.background = styleTexture;
		GUI.Box(new Rect(positionLeft + textureWidth + 10, positionTop + textureHeight + 10, 30, 30), new GUIContent(""), style);
	}

}

Nico, Look the wonderful ColorHSV script made by MatthewW here:
http://forum.unity3d.com/threads/create-random-colors.12031/#post-84625