Mach Bands
An illusion where uniform-color bands appear to have lighter and darker edges at each boundary, caused by lateral inhibition in the retina.
What it means
When adjacent bands of color transition in discrete steps from dark to light, your visual system exaggerates the contrast at each boundary. The lighter side of each edge appears even lighter, and the darker side appears even darker — creating the illusion of subtle gradients within each band, even though they're uniformly flat.
This effect, described by physicist Ernst Mach in 1865, is caused by lateral inhibition: neurons in the retina suppress the activity of their neighbors. At a boundary, cells on the light side are inhibited less (because their dark neighbors fire less), making them appear brighter. Cells on the dark side are inhibited more (because their light neighbors fire strongly), making them appear darker.
Why it matters in palette design
Mach bands directly affect how tint/shade scales look in design systems. When you generate a scale of evenly spaced lightness steps (e.g., 50 to 950), each swatch looks internally uneven — lighter at the edge bordering its darker neighbor, darker at the edge bordering its lighter neighbor. This is a perceptual illusion, not a rendering error, but it can make mathematically perfect scales appear poorly calibrated.
Example
A design system's gray scale shows 10 swatches from white to black in even OKLCH lightness steps. Designers reviewing the scale report that each swatch 'has a gradient' — lighter on the left, darker on the right. Adding thin borders between swatches or overlaying the actual hex values confirms the swatches are flat. The perceived gradient is Mach banding.
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Apply this to your palette
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