Elements that share visual properties are perceived as a group

The Gestalt law of similarity holds that items sharing shape, colour, size, or texture are automatically grouped by the viewer even when they are far apart. This is the basis for design system consistency: making all primary buttons the same colour signals ‘these are all actions’. Breaking similarity — making one button a different colour — draws the eye immediately and is the right technique for a call-to-action. Similarity can be created by any shared attribute (shape, value, orientation, texture, motion), and the brain will use whichever attribute is most salient in context.

Examples

A grid of grey squares with one row in blue — the blue row pops as a group. All hyperlinks underlined in blue on a webpage are perceived as ‘things you can click’.

Assessment

Design a navigation bar where links are perceived as one group and a logout button as a separate, danger-level item, using only similarity and proximity (no text labels).