It is very hard or impossible to come to a car store to buy a car and go back with that car home in one day. You must first make an order and wait for months(usually 4-6) while your car be ready.
Moreover, if you want to buy a car from foreign manufacturers (Mersedes-Benz, BMW, Toyota, etc) you have to pay 2X of its original price.
Some said it was because it is better at keeping the cars cool, but this doesn't explain why surrounding Kazakhstan/Tajikistan/etc had different color cars.
The best explanation I heard was the president liked white cars, so only allowed white cars to get made. This seems most plausible to me, and seems like similar things happened in Turkmenistan: https://www.motor1.com/news/226932/turkmenistan-president-ba...
But usually when my friends wanted to buy a car, they chose the white color by the following criteria: it does not heat much like other colors on the sun. If we take into account that there are not much parking lots and garages with a roof, white colored car is the best choice.
BTW: "shapka" or "шапка" (from Russian) is translated to English as a "hat" or "cap". That means, when you buy a thing, you need to also pay for its hat too.
Funny, in Norway it's more like 3X.