In his home city of Stockholm, Krikortz also show the results of his survey as different coloured lights on the side of a large building in the city. For example, red means the people of Stockholm are very happy. green is OK and purple means many people are sad. 'A lot of people look at the building every day and see how "we" are,' Krikortz says. The coloured lights are also useful if you feel like visiting the city. For example, if the lights are red, you know he locals are feeling happy!