That's only one of them, the default palette used by VGA cards. But there's another one, the one used by vt100 terminals and internally by linux. That one has the red and blue bits swapped, like 0=black, 1=red, 2=green, 3=yellow, 4=blue etc. I know this because this second scheme is used by the \e]P palette changer escape sequence. (This is btw another proof why this is not the real color/number correspondence: that's only the deafult palette, you can change it to whatever you like. I've rebound magenta to orange once to display Rubik's cube patterns nicely.) The translation table between the rgb and bgr scheme is color_table in /linux/drivers/char/console.c.

Update: see also Re: What is the Perl Color?.

This is btw another proof why this is not the real color/number correspondence: that's only the deafult palette, you can change it to whatever you like

VGA cards use it as the default for backward compatibility. It was introduced by CGA cards, and on those it was not merely the default and could not be changed; it was hardwired. (CGA cards did not have any way to display a color given arbitrary red/green/blue values. They *only* had the sixteen colors, ever, period. As an added bonus, you could only get more than four of them on the screen at once in text mode (although there were tricks available to make text mode appear to be a low-res graphics mode).)

I was pretty sure the CGA colors also match the ANSI colors, but I shouldn't be surprised that the VT100 used a different scheme; DEC did a lot of things differently from the rest of the world, such as using Category 4 (not 3, not 5) cable and MMJ connectors for networking, or the extraordinarily wacky way VMS expresses directory paths.

It was introduced by CGA cards, and on those it was not merely the default and could not be changed; it was hardwired.

Yes, you are right in this one. I do not know which of these numbering schemes was the first, any of them might predate ansi or vt100 terminals or cga cards as far as I know. (ZX spectrum seems to use 0=black, 1=blue, 2=red, 3=magenta, 4=green if this emulator is right.)

As an added bonus, you could only get more than four of them on the screen at once in text mode (although there were tricks available to make text mode appear to be a low-res graphics mode).

(Update: I was wrong here, see jonadab's reply) I think this is wrong. There is a low-resolution color mode of size 160x100 pixels (lines are doubled), 16 colors. That mode, however, is not supported by the bios, and the resoultion is very small (that's easy to say now, sitting at an 1280x1024 tft screen, mind you), so I guess only few programs used it.

Update 2015-12-01: see also https://en.wikipedia.org/wiki/List_of_color_palettes.

Or have I read one RS catalogue too many?

You really don't want to know the mnemonic my high school physics teacher gave us to remember the color codes on resistors.

Heh. BB.ROY of Great Britain had a Very Good Wife?

That's what I had as a mnemonic back in school when I learnt this!