  We observe a strong reverse saturation of absorption in ruby at a wavelength
of 473 nm. With an intensity-modulated laser, we observe that the peaks of the
pulses appear more than a hundred microseconds earlier than the reference
signal. A theoretical model based on coherent population oscillation would
suggest a fast-light effect with an extremely large and negative group index of
$-(1.7\pm0.1)\times 10^6$. We propose that this pulse advancement can also be
described by time-dependent absorption of ruby. Our study helps to understand
the nature of the fast- and slow-light effects in transition-metal-doped
crystals such as ruby and alexandrite.
