The first in a series of designs based on flow fields - every point on the canvas corresponds to a direction (this is created using two-dimensional simplex noise); a stroke starts at a random point on the canvas and travels in the direction of that point corresponds to, landing on a new point and following its direction, and so on, creating a curving stroke. You can read more about flow fields and their uses in generative art in this excellent essay by Tyler Hobbs.
In this design the colour of each stroke is determined by its length, strokes thicken as they follow the path of the field, and stop when they come near another stroke. Each stroke being a slightly different colour made it a lot easier to distinguish between different areas of colour than in previous block-colour designs, although the often-minimal difference in shades sometimes required a lot of squinting to differentiate.