def background_color(self, node, depth):
        """Create a (unique-ish) background color for each node"""
        if self.color_mapping is None:
            self.color_mapping = {}
        color = self.color_mapping.get(node.key)
        if color is None:
            depth = len(self.color_mapping)
            red = (depth * 10) % 255
            green = 200 - ((depth * 5) % 200)
            blue = (depth * 25) % 200
            self.color_mapping[node.key] = color = wx.Colour(red, green, blue)
        return color
Create a (unique-ish) background color for each node