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Anthocyanins are natural pigments known for their pronounced pH-dependent color changes, making them promising candidates for rapid, visual detection systems. In this study, anthocyanin extract from red cabbage (Brassica oleracea var. capitata f. rubra) was prepared using a 1:2 (w/v) ratio in 25% ethanol, followed by vacuum evaporation and application to two experimental systems: (i) a pH series ranging from 4.0 to 12.0, and (ii) Dulbecco’s Modified Eagle Medium (DMEM) under different sterility conditions (sterile, contaminated, and cell-containing). Color changes were quantified using spectrophotometry (570–630 nm) and image analysis with ImageJ. Results indicated a strong correlation between pH increase and changes in RGB mean values, with a marked shift in hue under alkaline conditions. In DMEM samples, contamination resulted in noticeable reductions in red, green, and blue intensities compared to sterile media, indicating potential for detecting contamination. This work demonstrates that anthocyanin-based sensors can visually and quantitatively detect pH variations and contamination in cell culture media, offering a rapid, low-cost, and sustainable approach for routine laboratory monitoring.