1. A method for displaying a thermal image ( 10 ) in an infrared (IR) thermal camera ( 1 ), comprising the steps of: registering an outdoor temperature value (T A ); registering an indoor temperature value (T B ); calculating an isotherm level (T ISO ) by using the registered temperature values (T A , T B ) and a temperature color alarm level (T CAL ); imaging a surface area to create an image of the temperature distribution in at least a part of the surface area; comparing the surface area temperature in at least one image point of the thermal image ( 10 ) to the isotherm level (T ISO ); adjusting the color of the at least one image point in dependence of the relation between the surface area temperature in said at least one image point and the isotherm level (T ISO ); and displaying the colored thermal image ( 10 ).