x.rb

class Proxy
  def initialize(document, style)
    @document = document
    @style    = style
  end

  def text(string, params)
    params[:size]  ||= @style[:font_size]
    params[:color] ||= @style[:font_color]

    @document.text(string, params)
  end
end


doc = Proxy.new(Prawn::Document.new, :font_size => 12, :font_color => "ff00ff")

doc.text("Hello World!")