This isn't the definitive, because the model # is one digit off, but if you Google for the datasheet for the Sharp color LCD panel's part number listed in the parallel thread to this you'll find one for a panel that appears to be identical and that datasheet says it's 12 bit (4 bits per channel) color. It's also worth noting that the "Service Source" hardware manual for the 500 series repeats that "16 greys" claim.

On the flip side, the "Developer Note" for the 500 series has a confusing section talking about the CLUT's 16 bit color mode and explains how they've especially optimized yadda yadda blaw blaw blaw so the video system will avoid attempting to display certain colors which don't render properly on the LCD, with that the end result is that the passive color displays can show a range of "about 4000" colors, while the range for the TFT displays is "around 24,000".

The display controller IC contains a 256-entry CLUT. Although the CLUT supports apalette of 32,768 colors, many of the possible colors do not look acceptable on the display.

Due to the nature of color LCD technology, some colors are dithered or exhibit noticeable

flicker. Apple has developed new gamma tables for these displays that minimizes flicker

and optimizes available colors. With these gamma tables, the effective range of the CLUT

for the active matrix color display is about 24,000 colors; for the DualScan color display,

the effective range is about 4000 colors.

Click to expand...

That latter number is bigger than 12 bits, which implies that even *if* the LCD's interface is only 12 bit the video hardware may do some sort of time-based multiplexing/dithering to increase the available color range (resulting in the "flicker"?). Perhaps that's the source of the "64 grey" claim, *or* perhaps whoever typed that up confused something between the LCD's capabilities and the external video port. (15/16 bit "highcolor" DACs, which is what the developer note says the CLUT is part of, usually only had 6 bit DACs.) All we really know is the video hardware *logically* supports "256 greys".

(Unfortunately the manual doesn't actually have the pinout of the LCD connector so we can't count data pins.)

In any case, fretting about exactly how many greys an 18 year old laptop does or does not display is probably a little silly in the grand scheme of things.