HS 5 SG have all the features of standard HS 5 (originally in black or white finish) except that these are limited edition colour. I've heard before about HS 5's flat representation of sound. I can confirm that they represent whole and flat sound image, without any saturation.
This grey colour shines on the light and gains a bit more light grey shade. In the dark they look more dark grey and conservative. Definitely, this grey outfit is the most interesting choice from HS 5's colour range today!