In order to investigation color change by hole blocking layer thickness in organic light emitting devices, hole blocking layer is inserted between two different emissive layers. As the thickness of hole blocking layer is increased, the color emitted from the device is found to change toward blue color via white electroluminescence after starting from orange color. The emission color could be controlled by the applied voltage and the thickness of blocking layer. The CIE coordinate of (0.30, 0.33) is obtained at an applied voltage of 14 V.