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The Commodore 64 has the following fixed palette of 16 colours:

C64 Colour palette

(Your palette may vary due to tuning of screen, etc.)

What was the reason for this selection of colours? Are these colours particularly easy to realise across a NTSC/PAL signal, or with the oscillator frequencies available in the C64?

(Alternatively, were these colours chosen due to non-hardware factors?)

This email from Robert 'Bob' Yannes indicates that the colours were arbitrarily selectable by the chip designers as a result of the design of the VIC-II.

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The email from Bob Yannes which you linked to gives the answer:

I'm afraid that not nearly as much effort went into the color selection as you think. Since we had total control over hue, saturation and luminance, we picked colors that we liked. In order to save space on the chip, though, many of the colors were simply the opposite side of the color wheel from ones that we picked. This allowed us to reuse the existing resistor values, rather than having a completely unique set for each color.

So basically it’s personal preference, with some consideration for technical constraints.

One aspect which often played a role in colour selection on early micros was luminance: you wanted a palette which would be usable on black-and-white TVs and monitors, which meant you needed distinct luma levels. This was apparently taken into account in later versions of the Vic-II which had eight different luminance levels instead of the initial four.

See What's with the Atari 2600 colors on SECAM? for a more “rational” palette construction.

  • I'm presuming they liked the first half of the colors since the second half is less flattering and as a whole was a bit muddy in comparison to other micros at the time. Despite the selection the VIC-II was a great chip for the era! – bjb Mar 19 '18 at 16:48

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