Actually, all Nikon bodies meter for ~12% gray (the 18% number is a myth that just keeps living--see my Web site or Bob Shell's book for more on this; and thank Ansel Adams for the confusion...).
The F5 and D1 models have a CCD sensor in the viewfinder that, in matrix metering only, is used to determine an adjustment to the metering based upon color. For example, mid-greens tend to be relatively close to the reflectance of gray, but mid-yellows aren't, so the camera would apply a slight modification to adjust for that difference. But in center-weighted and spot metering, the F5 and D1 models meter to gray.
Thom Hogan author, Nikon Field Guide author, Nikon Flash Guide author, Complete Guides to the N65, N80, and F100 author, Complete Guide to the Nikon D1, D1h, & D1x www.bythom.com
Thom Hogan author, Nikon Field Guide and Nikon Flash Guide author, Complete Guides to most Nikon cameras www.bythom.com