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Attribute clash was a display artifact caused by limitations in the graphics circuity of early colour 8-bit home computers - infamously the Sinclair ZX Spectrum.
The Spectrum's variant was caused by the idiosyncratic display memory layout. Rather than restricting the colour palette to conserve memory (the initial model of the Spectrum had only 16KB of RAM, which was used for the screen as well as program storage), Sinclair's design stored pixel and colour information separately, with colour information being stored at only the text character resolution - 32x24. Thus every 8x8 block of pixels could have only two colours - one foreground colour and one background colour (termed INK and PAPER in the Sinclair BASIC programming language).
Static graphic displays therefore had to be constructed with care. Finely-detailed colour graphics were impossible, as colour could only be applied in 8x8 blocks. Careful design could achieve impressive results, as could synchonising colour changes to the refresh rate of the display - a television set.
However, animated displays were more difficult - a distinct drawback in a machine whose primary use was video gaming. If just one pixel in an 8x8 block was recoloured because a moving part of the display touched it, the entire block would change colour. Thus detailed moving graphics caused large ugly fringes of rapidly-changing colours to follow them around.
Early software simply ignored this. Later, the standard workaround was to use colour for static display elements - such as a decorative border around the edges of the screen, which might include score displays and so on, or some form of instrumentation - with a smaller central monochrome area containing all the animated graphics. This also made graphics faster, as less of the screen had to be updated - both a smaller region, plus only changing pixel information and leaving the colour area untouched.
However, some late Spectrum software, such as FTL's Lightforce, used extremely careful graphics design to achieve full-colour moving graphics, essentially by restricting both the design of the onscreen elements and their paths of motion to 8x8 colour resolution boundaries. The moving elements were thus relatively large and rather blocky or squarish, and their movement was constrained, but this was not visually obvious and the sight of moving full-colour graphics was hugely impressive to Spectrum owners, who were long used to mocking jibes from owners of machines capable of animated full-colour graphics such as the much more expensive Commodore 64.
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