Validates a hexadecimal color value

hex_color_validator.rb

class HexColorValidator < ActiveModel::EachValidator
  def validate_each(record, attribute, value)
    record.errors[attribute] << (options[:message] || 'is not a valid colour value') unless self.class.matches?(value)
  end

  def self.matches?(value)
    return false unless value
    /\A#(?:[0-9a-f]{3})(?:[0-9a-f]{3})?\z/i.match(value).nil? ? false : true
  end
end