Some experts are so convinced that colours have a strong effect on us that they believe colours can be used to heal. Yellow stimulates the mind and creates a positive attitude, so it can help against depression. Green, which has a calming and restful effect, is supposed to be good for heart conditions. Books are now available that teach people how to heal with colour. These books provide long lists of ailments and the colours that can heal them. Some psychologists and physicians also use colour to help them treat patients with emotional and psychological problems.