def add_color(node, key = nil)
      key ||= node.expr.to_s

      self.colors[key] ||= { :variables => [], :alternate_values => [] }
      self.colors[key][:variables] << node.name

      self.colors[key][:alternate_values] |= ([node.expr.to_sass, node.expr.inspect] - [key])
    end
def add_color(node, key = nil)
      key ||= node.expr.to_s

      self.colors[key] ||= { :variables => [], :alternate_values => [] }
      self.colors[key][:variables] << node.name

      self.colors[key][:alternate_values] |= ([node.expr.to_sass, node.expr.inspect] - [key])
    end
add found color to @colors