We present a 3D label-free refractive index (RI) imaging technique based on single-exposure intensity diffraction tomography (sIDT) using a color-multiplexed illumination scheme. In our method, the chromatic light-emitting diodes (LEDs) corresponding R/G/B channels in an annular programmable ring provide oblique illumination geometry that precisely matches the objective's numerical aperture. A color intensity image encoding the scattering field of the specimen from different directions is captured, and monochromatic intensity images concerning three color channels are separated and then used to recover the 3D RI distribution of the object following the process of IDT. In addition, the axial chromatic dispersion of focal lengths at different wavelengths introduced by the chromatic aberration of the objective lens and the spatial position misalignment of the ring LED source in the imaging system's transfer functions modeling are both corrected to significantly reduce the artifacts in the slice-based deconvolution procedure for the reconstruction of 3D RI distribution. Experimental results on MCF-7, Spirulina algae, and living Caenorhabditis elegans samples demonstrate the reliable performance of the sIDT method in label-free, high-throughput, and real-time (∼24 fps) 3D volumetric biological imaging applications.