Amaranthus caudatus, known as amaranth or kiwicha, is a pseudocereal that does not contain gluten; it is a rich source of high quality nutrients, with a good amount of proteins, lipids and fiber; it also contains twice as much calcium as milk, all of which makes it an excellent input for the food industry. Within the research related to the development of products for this industry, many sustainable processes are being carried out using microorganisms, including filamentous fungi that produce red biopigments such as Monascus ruber, which provide added value to the substrates metabolized by fermentation. The objective of this study was to produce kiwicha flour fermented by M. ruber through solid-state fermentation. For this purpose, an optimization of factors such as the sodium chloride g/g–glucose g/g ratio (water–sample ratio) was carried out through a Box–Behnken experimental design because it comprises a specific set of 3k factorial combinations and is widely used in food processes due to its economic design. The fermented flour was analyzed in CIELAB color space (L*, a*, b*) and statistical analysis was performed using R software. The results of the optimized dependent variables were L*=51.93, a*=20.91 and b*=21.89 with R² values of 0.89, 0.87 and 0.88 respectively. The present study could provide a new and good source of flour with high added value in the food industry.