bpo-36176: Fix IDLE autocomplete & calltip popup colors. (#12262)

Prevent conflicts with Linux dark themes
(and slightly darken calltip background).
diff --git a/Lib/idlelib/calltip_w.py b/Lib/idlelib/calltip_w.py
index 7553dfe..1e0404a 100644
--- a/Lib/idlelib/calltip_w.py
+++ b/Lib/idlelib/calltip_w.py
@@ -80,7 +80,8 @@
     def showcontents(self):
         """Create the call-tip widget."""
         self.label = Label(self.tipwindow, text=self.text, justify=LEFT,
-                           background="#ffffe0", relief=SOLID, borderwidth=1,
+                           background="#ffffd0", foreground="black",
+                           relief=SOLID, borderwidth=1,
                            font=self.anchor_widget['font'])
         self.label.pack()