Demonstration which follows deals with the problematics of reproduction of black color in digital printing techniques. In addition to a comprehensive theoretical basis, and explanations, a major experimental section is subjective and objective measurement of the squares on which they are printed differently mixed black colors. It was printed in electrophotography and ink jet technology on two different substrates, the specialized substrate for each technology and ordinary office paper. Subjective part of the experiment was conducted among 10 men and 10 women aged from 18 to 50 years, with an average healthy vision; and objective part of the experiment consisted of the measurement of L * a * b * values of the prints with the spectrophotometer. The task for respondents was to sort the black boxes from the blackest to at least black, in each technique separately. The results were compared with those obtained by measuring with spectrophotometer. Due to the existence of so far not defined the standard recommended values for optimal mixing black color from the CMYK palette, neither for electrophotography nor for ink jet, as a reference point to calculate the value of ΔE obtained for the extremes, taken the average value of spectrophotometric measurements for electrophotography and ink jet. Final results represent the optimum relation of components of the CMYK palette in electrophotography and ink jet technology, on the specialized substrates for specific techniques, as well as ordinary office paper. Assumed that the results of this experiment and supporting elaboriration about them to be useful support for any print shop which in it work meets with the problems of reproduction of black color when printing in digital techniques, but also as a stimulus for further experiments of similar type, with the process, and other colors, as well in other non impact printing techniques.