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Attribute clash is a display artifact caused by limits in the graphics circuitry of some colour 8-bit home computers, most notably the Sinclair ZX Spectrum, where it meant that only two colours could be used in any 8×8 tile of pixels. The effect was also noticeable on MSX software and in some Commodore 64 titles. Workarounds to prevent this limit from becoming apparent have since been considered an element of Spectrum programmer culture.
This problem also happens with the "semigraphic modes" of the Color Computer and Dragon, but those computers also have non-attributed graphics and with better resolution. Several video game consoles of the era had such video modes that caused such limitations, but usually allowed more than two colours per tile: the NES had only one mode, which was also "semigraphic", and allowed four colours per 16×16 "block" but 16 per screen. The Super NES allowed 16 colours per tile but 256 per screen , and this made the artefact much harder to notice, if at all.