Arrgghh. My internet connection has gone from bad to worse (hence my sparseness here) and after an hour, it has only loaded part of Marjolein's blues.
The eyes do start out bright blue, yes, and turn amber with age. Quite cool, really.
On the mask, Marjolein, it says that a black mask is
perferred. Otherwise, it says that the dog has dark stripes on a light background. The nose should be black, but a blue nose (yup!) is hard to tell apart from black, unless you have them side by side with a black dog. Blue is specifically listed as an allowed color on the rough haired version. (and hardly any of them are really blue) It is mostly the requirement for a dark eye that would leave the blues out of the winners circle in the show ring.
But none of the characteristics of the blues are actually disqualifying faults at this point. A blue could not win, but a blue could pass, provided it is an othewise good specimen, of course.
Let me try to find my own
blue collection.
Your turn Juut!
Judith Van Neerland Dutch Shepherds 
Blues seem to have a following, though. I personally accept them readily, but would not select for it, afraid of CDA (= blue dog disease: possible hair loss on the eumalanin) I have not really seen it in DS's but it does affect most breeds that allow blue. Since the DS has eumalanin (black) and pheaomelanin (red) mixed through it's coat, it would not likely be a big problem like in for example dobermanns, who have entire black colored sections that would be prone to hair loss. But anyway. I know that Asheley has also had some blues (Pics Ash!!!) 
and maybe she can comment on the CDA risk.
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