CHROMA. a content-based image rctl-ieval syslem lhas inlroduced a perceptual color modcl, which can siinulatc the visual perceplual process of lhuman beings and eliminate ihe l~roblem ol condilional color variations. Th~s model Ihoweve~ rcgarded shadows and rcllcctions as u n k ~ ~ o u ~ i colors. and took no account of ihe inforclation which can bc gamed from them Th~s ~tudy atlempls Lo estnnale (he unbhown colors using i~ght~ng dil-cclions and lo prove that the process ol unknown colol eslimation can enhance the lperformance o l image retrieval syslems. With the ckperimcntal results, it was concludcd that thc model pmposcd in this study can enhance the perfomancc of content-based image retrieval systems using Lhe ]~ercepiual color model.