gistfile1.rb

Prawn::Document.generate "conditional_formatting.pdf" do |pdf|
  data = [["foo", "bar"],
          ["",    "baz"]]

  pdf.table(data) do |t|
    t.column(1).style do |c|
      if t.cells[c.row, 0].content.empty?
        c.text_color = "ff0000"
      end
    end
  end
end