Volumetric direct solar receivers have been proposed in Concentrated Solar Power (CSP) applications since they present higher efficiencies than standard surface receivers do. Silicon dioxide sand has been proposed as heat transfer and thermal storage material in Concentrated Solar Power (CSP) applications. Fluidized sand can be used in volumetric direct solar receivers; however, in this case, sand should be colored in order to improve its optical absorption properties in the solar spectrum. In this work, two methods are proposed and compared to colour the sand: Carbon Black (CB) nanoparticle coating and glucose degradation. The optical absorption is characterized using a double-beam UV-VIS spectrophotometer (Spectrophotometer Cary 500) before and after the fluidization. Moreover, colored sand shows no change in optical properties after 24 hours of fluidization, showing the practical applicability of this approach.