A crayon was a tool used for drawing, especially by young children. One of the colors available was royal blue.
Crayons
In 2369, a de-aged Ro Laren drew a picture of her mother with crayons. Guinan remarked to her that the wonderful thing about crayons was that they could take you to more places than a starship could. (TNG: "Rascals")
Crayons box
In 2380, Ensign Beckett Mariner and Brad Boimler were handing out crayons and other art supplies to Betan children on the streets of Beta III. (LD: "No Small Parts")