PDF::Writer：PDF::SimpleTable#shade_color2, #shade_color2=

require 'pdf/simpletable'

pdf = PDF::Writer.new

PDF::SimpleTable.new do |tab|
  tab.column_order = %w(col1 col2 col3)

  p tab.shade_color2
  tab.shade_color2 = Color::RGB::Blue
  tab.shade_rows = :striped
  tab.show_lines = :all

  data = [
    { "col1" => "foo1", "col2" => "bar1", "col3" => "baz1" },
    { "col1" => "foo2", "col2" => "bar2", "col3" => "baz2" },
    { "col1" => "foo3", "col2" => "bar3", "col3" => "baz3" },
  ]

  tab.data.replace data
  tab.render_on(pdf)
end

pdf.save_as("2008040600.pdf")

で、

#<Color::RGB:0x40252804 @r=0.7, @b=0.7, @g=0.7>

SimpleTable#shade_rows が :striped のときに使われるものらしい