So many buildings built in neo-classical style in cr. 1800-1850 in Russian empire are yellow (always the same shade of yellow) with white columns. There are some exceptions, e.g. grey or blue of beige with white columns, but maybe 90-95% of buildings built in this style are yellow and white, like on the first picture.
Was this colour scheme specific to Russian Empire or was it used elsewhere?
Why was it used in the first place? Antique buildings were all white when discovered, and originally they were brightly coloured (see the example of Parthenon below), I am not aware of such pastel-with-white-details colour scheme used in the antique world (was it?)