Color-color diagrams of all the YSOs identified in the fields of both DR 18 and ECX 6-21. The two examples shown here are respectively dominated by the effects of extinction (K_S − I1, J − H) and circumstellar excess (I2 − I3, K_S − I1). Red circles are Class I sources, blue diamonds Class II sources, green triangles transitional sources, and magenta squares Flat Spectrum sources. Sources of the same type tend to cluster on specific regions of each diagram, which nevertheless overlap due to our simultaneous use of all the available photometry to derive the spectral index, n, on which our classification is based.