ProGel food colouring
The Naughty Cook regularly uses ProGel food colouring products by Lancashire UK-based company Rainbow Dust which was founded in 2008 by three people passionate about supplying cake decorators with edible glitter having themselves been let down by poor service from other companies. Over the years, their efficient service has allowed them to expand their product range well beyond glitter and they now employ around 30 staff in a 20,000 square feet SALSA approved factory. They only supply the trade so home bakers need to go to suppliers such as those listing on Amazon  to find them.
We recommend their professional grade food colouring gels over liquids as they are highly concentrated and you only need to use very small amounts to achieve good results, which means you don’t end up with a bitter taste. They are especially good for things like macaroons.
You can add tiny amounts to sugar paste, marzipan, buttercream and suchlike and mix it in. The gels come in colour co-ordinated clean and easy to use plastic tubes with a tamper evident seal under a screw top. Easy to keep in your tool box, they can be quickly identified from the 37 tube colours. They can be bought as a complete set of 37, or as subsets, or individually for around £2.50 each.
The individual tubes might appear smaller than expected but bear in mind that a very little goes a long way.
These are probably the best of its kind on the market.