I would be grateful if you could give me any advice on how to get the grey-green of willow trees and the silvery grey of populars. I have tried various combinations but cannot get a really satsifactory colour. I have not so far used white in watercolour.

David Bellamy replies: An excellent colour for producing the silver-green and grey-green of willow trees and poplars is Terre Verte, produced in both Daler-Rowney and Winsor & Newton artists' quality watercolours and oils. By mixing other colours with it many subtleties of colour can be achieved.