Spectral photon-counting CT (PCCT) is a new emerging technology in the field of spectral imaging. It makes use of energy-resolving detectors, called photon-counting detectors (PCDs), recently integrated into clinical CT platforms. PCDs are made of semi-conductive material which makes it possible to convert incoming photons directly into electrical charges which migrate into a counting (application-specific integrated circuit, ASIC). The ASIC shapes a voltage pulse proportional to the incoming photon energy, and each photon can be differentiated in amplitude according to its energy. The transmitted spectrum can thus be characterized into multiple energy bins as defined by their different energy levels. In comparison to dual-energy CT abilities, SPCCT has the potential to provide more complete, accurate sampling of the energy dependence found in the CT images. Many advantages still in current development can be expected. However, it is worth mentioning that PCCT opens up an extended approach to spectral imaging by first improving the energy separation between high and low energy photons. This offers greater resolution of photoelectric and Compton contribution/absorption coefficients that will enhance the current known spectral capabilities such as virtual monochromatic images (VMI). The second benefit will be that additional materials can be added to the spectral decomposition of the images based on their K-edge energies, i.e., the binding energy between the K-shell and the nucleus. This approach, referred to as color K-edge imaging, is a real breakthrough in CT post-processing and comes with the promise of being available in the next generation of clinical Spectral PCCT systems. It mainly promises to overcome the limitations of dual-energy CT technology which cannot specifically or quantitatively separate different materials in the same voxel (or spatially co-registered), such as iodine and calcium. These images will soon be offered to radiologists together with the conventional HU-image which is impossible with conventional CT or dual-energy CT. K-edge imaging is comparable with the nuclear imaging twin modality of PET-CT where low-resolution functional information on FDG uptake is superimposed on high-resolution anatomical information, opening a completely new CT approach for functional, molecular, or inflammation imaging and many other areas requiring exploration.