Simple, green, sustainable, portable, wearable, cheap, reversible, flexible, comfortable, real time and highly sensitive viscose (Vis) fabric was developed for visual colorimetric recognition of urea in fluids. Natural anthocyanin (Ac) spectroscopic probe extracted from red-cabbage as well as urease enzyme as a catalyst were subjected to co-encapsulation process into the matrix of the calcium alginate biopolymer, which in turn was immobilized in situ into viscose fibers as a host matrix. Calcium alginate nanocapsules were generated on viscose surface utilizing the anthocyanin extract in combination with urease enzyme as the interior materials and the crosslinked calcium alginate as a shell. This co-encapsulation process was carried out in situ employing the pad-dry-cure method under ambient conditions. Both high sensitivity and small molecular size of this anthocyanin probe made it suitable for encapsulation within calcium alginate nanoparticles biosensor assay (Vis-Ac). The anthocyanin receptor encapsulated into calcium alginate displayed ratiometric variations in the absorbance spectra to the degree of a 127 nm hypsochromic blue-shift from 567 nm to 440 nm with the increasing the total content of urea in an aqueous medium. The colorimetric changes of Vis-Ac were monitored between purple and greenish-yellow in relative to increasing the concentration of urea. Those colorimetric changes were studied using CIE Lab chromogenic parameters, UV–visible absorbance spectra and colorimetric strength (K/S). HPLC-MS was utilized to describe the colored solution extracted from red-cabbage. Transmission electron microscopic (TEM) images were used to explore the generated Vis-Ac nanocapsules to display diameters in the range of 50–65 nm. The morphologies of Vis-Ac immobilized on viscose fabrics were investigated with energy-dispersive X-ray patterns (EDS), Fourier-transform infrared spectra (FT-IR) and scan electron microscope (SEM). The current biochromic sensor barcode showed a comparatively quick responsiveness (6–9 min) with a detection limit in the range of 300–1000 ppm. The comfortability of the treated viscose was studied by exploring its bend length, air-permeability and fastness properties.