At one point, western AH/AI used a uniform background, typically black, with just white horizon line ie no colour difference between 'ground' & 'sky'.
To make ground & sky referencing easier to perceive the areas below & above the horizon were given different colours.
Western manufacturers chose light blue or grey coloured sky & dark ground (dark blue? Can't remember) with even later versions opting for a brown ground depiction.
Russian also opted for a different coloured depiction of ground & sky to enhance readability. In their case they chose a dark 'sky' & a light 'ground'.
Why? Only surmising here, but one possibility is that they were trying to represent night sky & snow covered terrain. It could be argued that this is a more commonly found condition of flight that requires the use of the instrument, since daytime allows the possibility of visual reference.
Considering that the Western style depiction (blue over brown) is only representative of sky/ground colouring under something like a cloudless day over a desert(ish) area who's to say which is more correct?
BTW, I seem to recall that Russian AHs don't use a moving horizon bar with a fixed a/c representation. Instead the horizon bar is fixed & the a/c moves.
Just a different frame of reference.
[ 15 August 2001: Message edited by: Tinstaafl ]