The lowering intake of organic dyes and their auxiliaries by employing nanoparticles for some special textile coloration is novel and interesting topic. Nonetheless, application of reducing, stabilizing and other chemical agents in textile nano-coloration is still undesirable from both environmental and human/aquatic life viewpoints. This research renders a facile technique for wool coloration through locally forming selenium nanoparticles using sodium selenite without using other chemicals. Being industrially enforceable, free from use of additional chemicals, showing photo-active ability to discolor the dyeing effluent and low-toxic colorant are the main privileges of the used method. The wool fabrics were colored light to dark orange depending on coloration time and concentration of sodium selenite. Also, the color fastness properties against washing, rubbing and acid/alkaline spotting of prepared samples were excellent. Moreover, the colored fabrics indicated reasonable bactericidal and fungicidal performances toward Escherichia coli, Staphylococcus aureus and Candida albicans (95, 70 and 100 %, respectively) and still remained compatible with human skin. The in-situ synthesis of selenium nanoparticles on wool fabric not only colored the wool but also promoted the UV-protecting performance by 61.82 %, photocatalytic activity through methylene blue discoloration under sunlight by 97.22 % and tensile strength by 11.27 %.