The effect of 0-7 T magnetic field on the low wavelength resolution photoluminescence (PL) spectrum used for the all-optical thermometry was investigated. The PL spectra averaged over randomly-oriented color centers at the temperature between 283 and 343 K were measured for the analysis. Approximately 0.1% increase in the PL intensity was found at the longer wavelength side of the zero-phonon line (ZPL) with increasing the field strength. Its effect on the evaluated temperatures using the ZPL relative peak intensity and peak wavelength was less than their uncertainties of 8.7 and 3.7 K at 293 K, respectively.