We removed the bluish of the natural ruby successfully by vacuum annealing, and measured the color evolution with annealing time and temperature. We varied the anneal temperature and time $800~1500^{circ}C$ and $3~26$ hrs, respectively. The color evolution of rubies with annealing condition was recorded by a digital camera and a color coordination visible spectrometer. We determined the optimum bluish eliminating annealing condition was $1500^{circ}C-3hr$, which conserving the natural inclusions. We suggest the bluish shrink with diffusion coefficient of $D=(5 imes10^{-3}){exp}(-200.000/RT)[cm^2/s]$. We propose the color of ruby may be determined as the identical red color if the color difference between two samples are less than 1.0, and the color difference nay be an auxiliary standard to evaluate the color of rubies.