Overview:The ideal for all gardeners is to have year-round colour in the garden. Carole talks to Martin Barker from Aberdeen University School of Biological Sciences about the science of colour, finding out how and why plants are the colour that they are and how plant colour affects us. Meanwhile, the harvest continues, and Jim's big beef tomatoes are bearing heavy fruit. Colin and Catherine Lockhart in Carnoustie are no longer able to keep their garden the way that they would like, so Brian steps in to make their garden low-maintenance and wheelchair-friendly while still having year-round colour. One of Jim's favourite phrases is 'every day is a school day' and he is always trying to find the ideal tomato-growing system. With that quest in mind, Jim visits retired engineer Steve Engel in Fettercairn. Jim learns how Steve has engineered a homemade invention that keeps his precious tomato crop at the optimum temperature day and night while producing an extraordinary and impressive yield.