The magnificent seven amateur artists are confronted with the tail end of a hurricane as they set up their easels on the bonnie but windy banks of Loch Lomond. Their challenge is to paint water and the many colours it reflects.With the wind howling, in the first task they must try to mix the perfect colours to capture a boat and its stormy reflections in the turbulent water. Mentors Diana Ali and Pascal Anson, as always, areon hand with hints and tips, which some of the artists choose to ignore at their peril.The masterclasses this week are all about mixing colours. Armed with just the primary paints, our mentors have two techniques to help the artists see and mix colour more accurately. For the mainchallenge, the painters move to a full, panoramic view of the loch, which is useful as that is exactly what the judges want to see on canvas. Can they capture the ever-changing colours of the sky, land and water, which at times disappear from view all together? No one said it would be easy.At a viewing, the results are seen by members of the public, who decide on their favourite artist to be catapulted to the semi-final. The rest must await the verdict of the judges, Lachlan Goudie and Daphne Todd OBE.Hosted by Mariella Frostrup and Rev Richard Coles, the search for the winner of the Big Painting Challenge 2018 starts to heat up.