change_color.rb

#!/usr/bin/env ruby

COLOR_FILE = '/Users/ehrenmurdick/bin/config/desktop-color'

require 'color'
require 'rmagick'
include Magick

if File.exist?(COLOR_FILE)
  color = Marshal.load(File.open(COLOR_FILE).read)
else
  color = Color::HSL.new(0, 60, 40)
end
color.hue += 2
File.open(COLOR_FILE, 'w') {|f| f.write(Marshal.dump(color)) }

image = Image.new(100, 100)
rgb = color.to_rgb
p = Pixel.new(rgb.red, rgb.green, rgb.blue)
image = image.color_floodfill(1, 1, p)

name = "#{COLOR_FILE}-1.png"
image.write(name)
name = "#{COLOR_FILE}-2.png"
image.write(name)

%x{osascript /Users/ehrenmurdick/bin/update-desktop.scpt}
%x{echo #{Time.now} > /Users/ehrenmurdick/bin/config/color-changed-at}

update_desktop.scpt

set thePic1 to POSIX file "/Users/ehrenmurdick/bin/config/desktop-color-1.png"
set thePic2 to POSIX file "/Users/ehrenmurdick/bin/config/desktop-color-2.png"
tell application "Finder" to set the desktop picture to thePic1
tell application "Finder" to set the desktop picture to thePic2