Magnitude differences between IRAC 1 and W1 plotted against IRAC 1 magnitudes for the 248 protostars detected in both bands. The dashed red line is the mean difference, and the dotted red lines show the mean difference plus or minus one standard deviation. The solid blue line shows the mean plus two standard deviations (1.01 mag), the outburst threshold. Labeled protostars exceed the threshold at this wavelength; the encircled protostar (HOPS 223) is the only one detected in both bands that exceeds the thresholds at all three wavelengths.