Blue #4 is a muted blue/grey with fine blue and silver shimmer
The Nailgirls site calls it a shimmering blue grey which I think is pretty dead on. As you can see it takes on an almost muted turquoise hue in bright sunlight.
Swatch shown is 2 coats, with no top coat.
I really like this colour, greyed out blues always float my boat.
And apologies, my ring finger seemed to pick up a ding - ooops.