Organic light-emitting diode (OLED) will possibly become the mainstream in lighting technology given that its features, such as self-luminosity, deflectivity, and penetrability, are different from those of common light sources. Studies on OLEDs have generally focused on the luminous efficiency of its components; however, selecting an optimum color mixing spectrum for OLEDs to apply on illumination has seldom been discussed. In this study, color mixing is conducted by combining two and three colors based on color mixing theory. Through screenings that employ related evaluation techniques such as chroma standard and color rendering, we identify a set of optimum color mixing spectra at different correlated color temperatures that will be evaluated via the color rendering index (CRI), the color quality scale (CQS), and the feeling of contrast index (FCI). The CRI and CQS of simulative OLED light sources exhibit better performance at correlated color temperatures of 3000, 3500, 4000, and 4500 K than those of standard light sources of the Commission Internationale de l′Eclairage, whereas the FCI is increased to a range of 3-30%. The illumination images of standard and simulative light sources can be reproduced by using multi-spectral imaging. In this study, we attempt to explain the research direction of colors, which should be discussed in future studies on OLEDs, by applying several methods to evaluate light sources as well as color-image rendition technology.