I wonder though, can blues can get too dark? I haven't taken pictures yet, but a couple of my pullets are almost charcoal-colored.
There's what the standard says (I don't know that), and there's your own preference too. If you like a particular shade, and the standard does not say otherwise, then you might as well aim for the shade you like.
If you have any in a reasonable driving distance from you that are APA or ABA sanctioned, they're a lot of fun to go to just to admire all the different breeds and varieties that are entered!
Following.