With the wide use of mobile devices, display color reproduction has become extremely important. The purpose of this study is to investigate the optimal color temperature for mobile displays under varying illuminants. The effect of the color temperature and the illuminance of ambient lighting on user preferences were observed. For a visual examination, a total of 19 nuanced whites were examined under 20 illuminants. A total of 19 display stimuli with different color temperatures (2,500 K ~ 19,600 K) were presented on an iPad3 (New iPad). The ambient illuminants ranged in color temperature from 2,500 K to 19,800 K and from 0 lx to 3,000 lx in illuminance. Supporting previous studies of color reproduction, there was found to be a positive correlation between the color temperature of illuminants and that of optimal whites. However, the relationship was not linear. Based on assessments by 56 subjects, a regression equation was derived to predict the optimal color temperature adjustment under varying illuminants, as follows: [Display Tcp = 5138.93 log(Illuminant Tcp) – 11956.59, p<.001, R2=0.94]. Moreover, the influence of an illuminant was positively correlated with the illuminance level, confirming the findings of previous studies. It is expected that the findings of this study can be used as the theoretical basis when designing a color strategy for mobile display devices.