Our digital holographic (DH) approach can be used to study tissue structures both in vitro and in vivo. This DHM architecture can produce three color microscopic 3D and 4D (video) images. We record 3 color (RGB) holograms with single exposures, and the perfect compensation of color crosstalk is solved. An in-line holographic setup and reconstruction algorithms are presented with demonstrative simulations and experimentally captured and numerically reconstructed images. Comparing the individually reconstructed color images with each other can provide information both for recognition of different types of cells or microorganisms, and for diagnostic purposes as well. Experimental example is given observing microscopic hydro-biological organisms using a color digital holographic microscope.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.