We present the most extensive and detailed reddening maps of the Magellanic Clouds (MCs) derived from the color properties of Red Clump (RC) stars. The analysis is based on the deep photometric maps from the fourth phase of the Optical Gravitational Lensing Experiment (OGLE-IV), covering approximately 670deg^2^ of the sky in the Magellanic System region. The resulting maps provide reddening information for 180deg^2^ in the Large Magellanic Cloud (LMC) and 75deg^2^ in the Small Magellanic Cloud (SMC), with a resolution of 1.7'x1.7' in the central parts of the MCs, decreasing to approximately 27'x27' in the outskirts. The mean reddening is E(V-I)=0.100+/-0.043mag in the LMC and E(V-I)=0.047+/-0.025mag in the SMC. We refine methods of calculating the RC color to obtain the highest possible accuracy of reddening maps based on RC stars. Using spectroscopy of red giants, we find the metallicity gradient in both MCs, which causes a slight decrease of the intrinsic RC color with distance from the galaxy center of ~0.002mag/deg in the LMC and between 0.003 and 0.009mag/deg in the SMC. The central values of the intrinsic RC color are 0.886 and 0.877mag in the LMC and SMC, respectively.