Quote Originally Posted by Graham
Matthews' Clergy looks darker that USAK Clark - or is it just the photo?
I think it is the actual fabric. Most mills vary in color, but I think these are further than "normal." The 16oz Lochcarron Clergy is clearly lt. blue, while the USA KILTS PV is a white. The descriptions of clark/clergy vary somewhat in the early tartan books, as different authors tried to interpret one another. The Clery Green is yet another variation of the same thing (with green stripes this time). The absolute earliest seems to have been the blue (which I believe was more of a turquoise), which was then interpreted as either white, blue, or green. Some books even refer to Clergy, Clergy Blue, and Clergy Green.

Matt Newsome (to many Matt's here) covers it well in this article:
http://albanach.org/clergy_tartan.htm
(Any differences would be from my forgetfulness this morning (5 am here) than from understanding.)

The manufacturers likely used to different sources for the coloring. Lochcarron adopted the more original light blue, while Marton Mills used the white variation.