When a colour is critical, the best way to communicate it is with the Pantone Colour Books. The books allow you to be confident that the swatch you're looking at in your book is the same as the swatch in your printers' book.
Pantone colours can be simulated on a computer or mobile device, but for true communication accuracy the best bet it to choose from a physical Pantone Book.
Here are some suggestions if you don't own a Pantone Book:
Contact a local design studio and ask if you can visit to choose a colour.
Visit your nearest print shop (including ours) and ask if you can have a look through their book to choose a colour.
Ask any designer or artist in your social network if they may have access to a Book.