title: ARGB in tkinter ttk behaves unexpectedly
body: <p>I've been trying to learn Tkinter and subsequently ttk to create a GUI. When working with ttk I noticed something peculiar happening. When I gave any colour in an ARGB format, <code>'#80FFFFFF'</code> for example, there was no error but the particular widget simply turned into a small square. Why does this happen?</p>
  
  <p>Here is an example, </p>
  
  <pre class="lang-py prettyprint-override"><code>import tkinter as tk
  from tkinter import ttk
  
  root = tk.Tk()
  
  s = ttk.Style()
  
  s.configure('b1.TButton', background='#FF0000')
  s.configure('b2.TButton', background='#80FFFFFF')
  
  b1 = ttk.Button(root, style='b1.TButton')
  b2 = ttk.Button(root, style='b2.TButton')
  
  b1.grid()
  b2.grid()
  
  root.mainloop()
  </code></pre>
  
  <p>This is the result of this code: <img src="https://i.imgur.com/f0rf4uN.png" alt="Imgur"></p>