The present invention relates to a method of infusing coloration in solder to facilitate inspection of soldered portions in the production of electronic machinery, equipment and apparatus, and further, a method of forming a colored membrane on the surface of the soldered portions by employing colored solder materials.Physically and chemically stable colored powders composed of rare earth compounds or metallic fluoride compounds, having properties of specific gravity lighter than that of solder and further being indecomposable even at a temperature higher than that of the melting points of solders, are mixed into flux. After soldering by employing solder cream containing the mixture, a colored membrane or layer may be formed on the surface of soldered portions by deposition of the colored powder compounds.