Color–color diagrams used for identification of Class I (left), and Class II (right) sources in phase 1 of the classification scheme presented by Gutermuth et al. (2009) for an example of GMF 39 (CFG047.06+0.26). The black filled circles represent the selected Class I and Class II sources. The remaining Class III/field sources are indicated by the gray dots. The black lines show the color criteria of the classification scheme.