In off-axis digital holographic microscopy, short coherence length of the source results in an unwanted reduced field of view. A diffractive optical element (DOE) which combines two high efficiency transmission volume phase gratings holographically recorded into a thin photopolymer, is proposed to manipulate the coherence plane tilt of beam containing a plurality of wavelengths simultaneously. The DOE extends the interference pattern between object and reference beams in digital holographic microscope (DHM) over the whole physical beam overlap area. We experimentally demonstrate full field imaging in a commercial, two colors (685 nm and 794 nm) reflection digital holographic microscope (DHM). The synthetic wavelength created by the two colors extends the unambiguous depth range of the DHM from 0.39 mu m to 2.49 mu m.