To investigate the influence of clinical factors (duration of diabetes mellitus, fasting blood sugar level, fructosamine concentration, and hemoglobin A1c) on blue-on-yellow (B-on-Y) perimetry compared with white-on-white (W-on-W) perimetry for diabetics without retinopathy. Both B-on-Y perimetry and W-on-W perimetry were performed for 33 diabetics without retinopathy. Thirty-three subjects with healthy eyes served as age-matched controls. For both diabetic patients and controls, mean deviation (MD) and corrected pattern SD of perimetry showed no difference irrespective of B-on-Y or W-on-W perimetry. For diabetics, MD of B-on-Y perimetry decreased in proportion to the morbid period with diabetes mellitus, with the same being true with deterioration of the clinical factors. Multiple regression analysis disclosed no differences in MD of clinical factors for W-on-W perimetry, despite the duration of diabetes mellitus exerting a significant influence on MD of B-on-Y perimetry. Even at the premorbid stage of diabetic retinopathy, longer duration of diabetes mellitus and longer persistence of poorly controlled diabetes mellitus are associated with an insidious progress of dysfunction in the retinal blue cone system.