For some samples, it has been shown that spectra of QSOs with low redshift are bluer during their brighter phases. For the FIRST bright QSO sample, we assemble their spectra from Sloan Digital Sky Survey Data Release 7 (SDSS DR7) to investigate variability between the spectra from White et al. and from the SDSS for a long rest-frame time lag, up to 10 years. There are 312 radio-loud (RL) QSOs and 232 radio-quiet (RQ) QSOs in this sample, up to z similar to 3.5. With two-epoch variation, it is found that the spectra of half of the QSOs appear redder during their brighter phases. There is no obvious difference in slope variability between subsamples of RQ and RL QSOs. This result implies that the presence of a radio jet does not affect the slope variability on 10 year timescales. The arithmetic composite difference spectrum for variable QSOs is steep blueward of similar to 2500 angstrom. The variability for the region blueward of 2500 angstrom is different to that for the region redward of 2500 angstrom.