Start in grayscale

Why this rule exists

Color is seductive, and that is exactly the problem. Reach for it too early and it becomes a way to fake hierarchy that the structure has not earned, papering over a weak layout with a bright accent instead of fixing the layout. Designing first in grayscale forces you to build hierarchy out of the durable materials, size, weight, spacing, and position, so that the screen already works before a single hue is added. If a layout reads clearly in black, white, and gray, color will only make it better; if it does not, color is being asked to do a structural job it was never suited for. Working monochrome first also protects you from the trap of using color as decoration, and it means the design will still function for the many users and contexts where color is muted, absent, or perceived differently. Prove the bones in gray, then add color as the finishing layer it should be.