Over-spray is usually an unobtrusive indigo, purple, blue or green ink that often appears on the upper edge and sometimes spine of a book. However, it is not uncommon to have a severe over-spray so that it becomes a visually obtrusive defect. It was common that distributors would code bundles of books by spraying the top edges with a colored liquid mist. This was done as a method of identification used by distributors so they would know which books were the ones they distributed (there were multiple distributors). Often books would be returned to distributors, and in the event of a return distributors only accepted books they originally distributed, and not books from other distributors.