In the world of art and illustration, "blue-line" sketching has become a popular technique, especially among digital artists. Originally, artists used "non-photo blue" pencils because their markings would remain invisible when photocopied, making it easier to create clean, crisp drawings. Today, even with digital tools replacing traditional photocopying, blue-line sketching is still widely used—mostly out of habit or for its practicality. The subtle blue lines provide a background structure that allows artists to layer pencil or pen over their sketches without the original lines interfering, giving them the freedom to refine and develop their work without distraction.