title: Python: change entry colour dynamically with Tkinter
body: <p>I am getting problems with Tkinter after() method.
  Actually, what I want to do is to change the background colour of some entry boxes as soon as times passes. Let's take this piece of code (which is different from the script I'm working on, but the situation described is the same):</p>
  
  <pre><code>import Tkinter as tk
  
  root = tk.Tk()
  root.option_add("*Entry.Font","Arial 32 bold")
  
  emptyLabel=tk.Label()
  emptyLabel.grid(row=4) #Empty label for geometry purpose
  entryList=[]
  
  for x in range(4):
      entryList.append([])
      for y in range(4):
          entryList[x].append('')
          entryList[x][y]=tk.Entry(root, bg="white",width=2,justify="center",
                                   takefocus=True,insertofftime=True)
          entryList[x][y].grid(row=x,column=y)
  
  solvebt=tk.Button(root,text='Solve').grid(row=5,column=2)
  newgamebt=tk.Button(root,text='New').grid(row=5,column=1)
  
  #BROKEN PART STARTS HERE 
  
  def changebg(x,y):
      entryList[x][y]['bg']='yellow'
  
  for x in range(4):
      for y in range(4):
          entryList[x][y].after(300,changebg(x,y))
          #Same result with root.after(300,changebg(x,y))
  
  
  root.mainloop()
  </code></pre>
  
  <p>The problem is that when I start the program, I would expect it to show me as it "paints", one at time, all of the entry boxes in yellow. What happens, instead, is that the program freezes for (300*16) milliseconds and then, all of a sudded, every entry boxes is yellow!</p>