With the development of tablet display technology, using tablet has become more and more popular for people to read news and messages. For enhancing visual comfort, many tablets are designed to change display brightness or color with surrounding conditions. Few studies, however, investigated how text-background lightness combination of a tablet should change when the color and light level of a surround change simultaneously, especially under very high light level (e.g., under daylight). In this study, twenty observers evaluated visual comfort of 20 text-background lightness combinations on an iPad Air 2 through paired comparisons under five surrounds—a dark surround and four ambient lighting conditions, comprising two levels of CCT (i.e., 3500 and 6500 K) and illuminance (i.e., 300 and 3000 lx). The observers judged the combination of black text with a light grey background (i.e., L*_background = 75.33 and L*_text = 1.6) the most comfortable when there was ambient light regardless of CCT and illuminance. This combination was also evaluated as the third most comfortable under the dark surround.