The web safe colours are web safe because they can be displayed on PCs with 8 bit video cards (yes, that was ages ago

) They're also called "non dithering colors".
Nowadays all colours are considered web safe, as they can all be displayed by modern graphics cards.
More:
http://www.lynda.com/hex.html (note the part on PDA's and such devices)
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Added: There's also the Windows 16 color VGA palette:
http://www.w3.org/TR...ypes.html#h-6.5---
Added (II):
I just have to mention the ColorZilla firefox plugin:
http://www.iosart.co...fox/colorzilla/It's not mine, it's not anyone I know, it's non commercial, and nobody pays me for saying this: It's just a very simple and very useful little tool.