Secret colours of the Commodore 64
As an Australian user of the TRS-80 Color Computer I was always disappointed the artificating technique:
<a href="https://en.wikipedia.org/wiki/Composite_artifact_colors" rel="nofollow">https://en.wikipedia.org/wiki/Composite_artifact_colors</a>
... didn't work on PAL so I never got to see all the 'cool' colours promised on game adverts in USA-based magazines!