gistfile1.rb

#file:  app/themes/blue/mixins/blue_users_controller_mixin.rb
module BlueUsersControllerMixin
  
  def blue_show
    #themed_show method here
  end
  
end

# app/controllers/users_controller.rb
class UsersController < ApplicationController
  
  before_filter :set_current_theme_mixin
  
  def base_show
    #original (default) show method
  end
  
  def method_missing(method_name, *args, &block)
    name = method_name.to_s
    if self.respond_to?("#{current_company.theme}_#{name}")
      self.send("#{current_company.theme}_#{name}")
    elsif self.respond_to?("base_#{name}")
      self.send("base_#{name}")
    else
      super
    end
  end
  
  private
  
  def set_current_theme_mixin
    if File.exists?(RAILS_ROOT, 'app', 'themes', current_company.theme, 'mixins', "#{current_company.theme}_#{params[:controller]}_controller_mixin.rb")
      @controller.extend("#{current_company.theme}_#{params[:controller]}_controller_mixin".constantize)
    end
  end
  
end