I found class << self, but still here's an even simpler example that 
doesn't work as I thought it would:

module Color
  def set_fill(color)
    puts "testing"
    @@fill_color = color
  end
end

class Shape

  @@fill_color   = 'black'

  class << self
    include Color
  end

  def self.fill_color
    @@fill_color
  end

end

Shape.new
puts Shape.fill_color

Shape.set_fill('red')
puts Shape.fill_color

I get:

black
testing
black

--gw

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