lekamu wrote:How does one achieve this effect on stones?

I want to assume you mean the lower part of the house. Get a good stone dresser and they will do it for you, in nairobi / central area are they call it "comb" style, not sure about the rest of the country.
If the upper part, you can plaster on the stone and paint plain or spray to give the desired effect. Wallmaster will also work.