The Brush tool is often the most intuitive and rapid tool for creating rough sketches and clean lines. A single colour, such as black, is often used when tracing a clean version of a rough sketch. However, when it comes time to soft trace the lines in different colours, the flattened or unflattened clean brush strokes can suddenly become time consuming to ink.
Toon Boom Harmony lets you create triangular breaks at line intersections. These intersections are the probable locations where colour line breaks naturally occur, such as where a sleeve meets a hand.