The paper first introduces the technical background of sub-pixel rendering (SPR) for RGBW4-primary color displays, describes the design of a versatile SPR simulator which can be used for testing visual effects of various SPR parameters, summaries the major findings of a psycho-visual experiment based on the simulator, and points out its color inaccurate problem. An adaptive sub-pixel rendering algorithm is then proposed for solving the problem. The proposed SPR algorithm is capable of improving color naturalness of an RGBW display with high brightness under higher visual resolution.