Colour Clash

Overview

The ZX Spectrum could display vibrant colours, but with a catch: each 8×8 pixel block shared one foreground (INK) and one background (PAPER) colour. When a sprite moved across block boundaries, it inherited the colours of whatever it overlapped. This “colour clash” defined the Spectrum’s visual character.

The attribute system

Component	Size
Pixel data	6,144 bytes (256×192 monochrome)
Attributes	768 bytes (32×24 colour blocks)

Each attribute byte controls an 8×8 block:

Bits 0-2: INK colour
Bits 3-5: PAPER colour
Bit 6: BRIGHT
Bit 7: FLASH

Why it happens

When a sprite crosses attribute boundaries:

Sprite pixels set in block A
Sprite also overlaps block B
Block B has different INK/PAPER
Sprite inherits block B colours
Visual discontinuity appears

Mitigation strategies

Monochrome sprites

Many games used single-colour sprites:

No clash visible
Consistent appearance
Knight Lore, Head Over Heels

Careful level design

Design backgrounds to minimise contrast:

Similar colours in adjacent blocks
Black backgrounds common
Strategic colour placement

Small sprites

Sprites smaller than 8×8:

Stay within single attribute
Limited visual impact
Restricts game design

Attribute-aligned movement

Move sprites in 8-pixel increments:

Always aligned to blocks
Jerky movement
Not suitable for action games

Notable approaches

Game	Strategy
Knight Lore	Monochrome graphics
Cobra	Coloured but careful
Rainbow Islands	Accepted clash
Renegade	Masked backgrounds

The “Spectrum look”

Colour clash became:

Defining characteristic
Nostalgic aesthetic
Recognised style
Design challenge

Comparison with competitors

System	Colour system
Spectrum	Attribute blocks
C64	Character cells (similar)
Amstrad CPC	Per-pixel colour
MSX	Attribute cells

Modern perspective

Colour clash is now:

Deliberately recreated in retro games
Nostalgic visual style
Design constraint appreciated
Historical interest

The Spectrum's curse