The coloRegex gem saves you from dealing with regex for colors, it contains all 148 named colors including transparent and currentColor.
And deals with any kind of color code: hex, rgb, rgba, hsl, hsla.

Nothing fancy here after installation you'll have a new constant available: COLOREGEX

class Person < ActiveRecord::Base
  validates_format_of :color, with: COLOREGEX, on: :create
end

Or:

'#FF0000'.match?(COLOREGEX)
#=> true
'#FF000Q'.match?(COLOREGEX)
#=> false

For bundler add it to your Gemfile:

gem 'coloregex', '~> 0.1.2'

For manual do:

$ gem install coloregex

##Todo:

• ?

• Your more than welcome to contribute; open up a pull request and i'll have a look.

The gem is available as open source under the terms of the MIT License.

• Thanks to Adil Yakubi for creating the cool illustration you see above.
• Thanks to all the commentators & contributors to this gist