We are developing enhanced volume rendering techniques for color image data. One target application is cryo-imaging, which provides whole-mouse, micron-scale, anatomical color, and molecular fluorescence image volumes by alternatively sectioning and imaging the frozen tissue block face. With the rich color images provided by cryo-imaging, we use true-color volume rendering and visually enhance anatomical regions by proper selection of voxel opacity. To compute opacity, we use color and/or gradient feature detection followed by suitable opacity transfer functions (OTF). An interactive user interface allows one to select from among multiple color and gradient feature detectors, OTF's, and their associated parameters, and to compute in live time new volume visualizations from within the Amira platform. We are also developing multi-resolution volume rendering techniques to accommodate extremely large (>60GB) cryo-image data sets. Together, these enhancements enable us to interactively interrogate cryo-image volume data and create useful renderings with "implicit segmentation" of organs.