Added color history (but only after using at least 4 different)

Paint_2/Form1.cs

@@ -17,8 +17,6 @@ namespace Paint_2
         List<PaintTool> toolList;
         bool drawing = false;
         Random rnd;
-
-        int debugCounter = 0;
         public PaintForm()
         {
             InitializeComponent();
@@ -42,14 +40,17 @@ namespace Paint_2
             sketch.StartDrawing(MousePositionToCanvasPosition(), Color.FromArgb(rnd.Next(0,256), rnd.Next(0, 256), rnd.Next(0, 256)), (int)nupPencilWidth.Value);
             tmrRefresh.Enabled = true;
 
-            //new Thread((sketch) => { (sketch as Sketch).AddDrawingPoint(this.PointToClient(MousePosition)); }).Start();
+            List<Color> colorHistory = sketch.CurrentTool.GetLastColors(4);
+            btnColorHistory1.BackColor = colorHistory[0];
+            btnColorHistory2.BackColor = colorHistory[1];
+            btnColorHistory3.BackColor = colorHistory[2];
+            btnColorHistory4.BackColor = colorHistory[3];
         }
         private void canvas_MouseUp(object sender, MouseEventArgs e)
         {
             tmrRefresh.Enabled = false;
             sketch.AddDrawingPoint(MousePositionToCanvasPosition());
-            sketch.Paint();
+            canvas.Image = sketch.Paint();
-            canvas.Image = sketch.Drawing;
             drawing = false;
         }
 
@@ -58,8 +59,7 @@ namespace Paint_2
             if (drawing)
             {
                 sketch.AddDrawingPoint(MousePositionToCanvasPosition());
-                sketch.Paint();
+                canvas.Image = sketch.Paint();
-                canvas.Image = sketch.Drawing;
             }
         }
     }

Paint_2/PaintTool.cs

@@ -18,6 +18,7 @@ namespace Paint_2
         void Start(Point point,Color color,int width);
         void Stop(Point point);
         void Add(Point point);
+        List<Color> GetLastColors(int colorNumber); 
         void Paint(Bitmap canvas);
     }
 }

Paint_2/Pencil.cs

@@ -66,5 +66,25 @@ namespace Paint_2
         {
             throw new NotImplementedException();
         }
+        public List<Color> GetLastColors(int colorNumber)
+        {
+            List<Color> result = new List<Color>();
+            if (Colors.Count <= colorNumber)
+            {
+                //We need to fill with black color
+                for (int i = colorNumber; i >= 0; i--)
+                {
+                    result.Add(Color.FromArgb(0x00,0x00,0x00));
+                }
+            }
+            else
+            {
+                for(int i = colorNumber; i > 0; i--)
+                {
+                    result.Add(Colors[(Colors.Count)-i]);
+                }
+            }
+            return result;
+        }
     }
 }

Paint_2/Sketch.cs

@@ -56,12 +56,13 @@ namespace Paint_2
         {
             CurrentTool.Add(location);
         }
-        public void Paint() 
+        public Bitmap Paint() 
         {
             foreach (PaintTool tool in ToolList)
             {
                 tool.Paint(Drawing);
             }
+            return Drawing;
         }
         public Color GetColor(Point location)
         {