I got an email from Germany.

nachbar.rb

module Mod
  def check_neighbour? a, b
    return true if @circles.empty?
    @circles.each{|c| return false if c.left/40 == a and c.top/40 == b}
    @circles.each do |c|
      x, y = c.left/40, c.top/40
      return true if (x-1 == a and y == b) or (x == a and y-1 == b) or (x+1 == a and y == b) or (x == a and y+1 == b)
    end
    return false
  end
end

Shoes.app :width => 640, :height => 400, :resizable => false do
  extend Mod
  background aliceblue
  # Spielfeld 8 x 8, Rechtecke
  @board = Array.new(8) do |x|
    Array.new(8) do |y|
      rect(x*40, y*40, 40, :fill => burlywood)
    end
  end
  @move = white
  @circles = []
  click do |c, x, y|
    a = x/40
    b = y/40
    if a <= 7 and b <= 7 and check_neighbour?(a, b)
      @circles << oval(a*40, b*40, 40, :fill =>@move)
      color = send COLORS.keys[rand(COLORS.keys.size)]
      @circles.each do |c|
        c.style :fill => color
      end if @circles.size > 1
    end
  end
end