What is a web-safe colour pallette?
Colours that are not web-safe have the potential to render incorrectly on low-colour displays.
Note that using web-safe colours will not have any effect on graphic backgrounds. Graphic backgrounds might be diffused in some situations, so you should be especially sure those are GIFs that use the web-safe palette.
Colours that are web-safe (hex values of 00, 33, 66, 99, CC, or FF), as are colours using the hex values of 11, 22, 44, 55, etc.
From a Macintosh user:
I fired up Netscape 4.7 on the Windows machine and double-checked that the display is set to 256 colours. The 11 greys do not all map to the web-safe greys. When examined with ColourPick (which I discovered in the intervening years) the greys map to:
100% ffffff to ffffff 91% e8e8e8 to fffbf0 87% dedede to cccccc 80% cccccc to cccccc 74% bdbdbd to c0c0c0 60% 999999 to 999999 52% 858585 to 808080 45% 737373 to 666666 40% 666666 to 666666 20% 333333 to 333333 0% 000000 to 000000
In Netscape 4.7 for Windows the 87% and 45% greys fail the test, so we'll make that 9 browser-safe greys for Netscape for Windows.
OTOH ColourPick can clearly distinguish all 11 greys in Internet Explorer 5.5 for Windows. I will not exhaust the readers further by laboriously listing the values I get for the 11 greys in Internet Explorer for Windows.
Netscape 4.78 for the Mac does clearly distinguish all 11 greys.
I will add that when it comes to images, instead of background colours, the greys DO map to the nearest web-safe grey in Netscape for both Mac and Windows, obvious when you look at the little grey apple place-holder in the 11 browser-safe greys table. Internet Explorer for both Mac and Windows does distinguish the 11 greys in both graphics and background colours.
There are definitely 16 greys in the Macintosh 256-colour system palette. My two Mac graphics programs disagree about what exactly the 256-colour Windows palette is, so I cannot verify how many greys there are in the Windows 256-colour palette. This Mac user is completely daunted by the prospect of trying to choke that information out of the old Windows machine. I leave that for the Windows users to find out (and I hope report back with said info).