Magnitude differences between IRAC 2 and W2 plotted against IRAC 2 magnitudes for the 260 protostars detected in both bands. The lines, the annotations, and the purple circle have the same meaning as in Figure 1, where the outburst threshold at this wavelength is 1.54 mag. The object encircled in orange is HOPS 383, which exceeds the threshold at two of three wavelengths and was not detected in the 3.6 μm Spitzer band.