> If not, is there any other ways to do it?
Not really, but there's a workaround.. you can use the Advanced tab of the Edit | Find by Query (Ctrl-F) dialog to find images of a certain color type:
tn.[colortype] = N
..where N is one of the following:
1: Grayscale (either 8-bit or 16-bit) or B/W (1 bit)
2: 8-bit color
3: 24-bit color
4: 32-bit color
255: unknown color type
Once you have found all images of a certain colortype, you can assign a user field value to them, which you can later sort on. Or, maybe you can make a gallery for each colortype.
The disadvantage is that this will only work for your existing images, and that you will have to repeat it when you add new images.
p.s. Version 10 does not seem to offer a way of directly sorting on colortype either. Its nicer interface, unicode support, SQLite3 support et cetera might still make it a nice upgrade though :) Until May 29, Cerious is offering licenses and upgrades at 30% off (Memorial Weekend sale) through this semi-secret link: [link=http://www.thumbsplus.com/orderpaypal_fb.shtml]FB SALE[/link].