Hydroxyapatite (HAp) becomes colored after heat treatment; however, the cause of this phenomenon is still unclear. The purpose of this study is to investigate the HAp synthesis conditions under which this phenomenon occurs. In the experiments, color was measured using a color meter and the colored HAp was identified by X-ray diffraction (XRD) analysis. The results show that HAp synthesized by wet process has two colors: red and reddish-brown. In the case of the red HAp, the concentration of red components varied from low to high. On the other hand, for the reddish-brown HAp, the concentration of reddish-brown components was almost constant. The red HAp was observed only when tricalcium phosphate (TCP) was not detected by XRD analysis and SEM.