class Preference < ActiveRecord::Base
    acts_as_array :colors # :separator => ',' (default)
    COLORS = [
      ['Red', 1],
      ['Blue', 2],
      ['Brown', 3]
    ]
  end

- form_for @preference do |f|
  %p
    = hidden_field_tag 'preference[colors][]', ''
    - Preference::COLORS.each do |c|
      = check_box_tag "preference[colors][]", c[1], @preference.colors.include?(c[1].to_s)
      = c[0]