Tiff 5.0 includes the following color Tags:
320 Color Map -- Defines the RGB color map for palatte color images.
-- New modes to handle Palette color and Greyscale
To get a Tiff Developer's ToolKit send $30 (includes postage) to
411 First Avenue South
Seattle, WA 98104 Or Call (206) 622 - 5500 for info
I've ordered one, but it hasn't come in yet.