Non-photo blue

Shade of blue not detected by film

Non-photo blue is a common tool in the graphic design and print industry, being a particular shade of blue that cannot be detected by graphic arts camera film. This allows layout editors to write notes to the printer on the print flat which will not show in the final form. It also allows artists to lay down sketch lines without the need to erase after inking.

This keyword could refer to multiple things. Here are some suggestions: