An image analysis method has been developed for measuring mixing times in stirred vessels. The method consists of capturing images of the flow patterns observed in the agitated vessel by use of a fast acid-base indicator reaction technique. These images are analyzed to quantify the color evolution by means of a hue, light, and saturation color model (HLS), which corresponds to mixing evolution. In comparison with other non-intrusive techniques based on the red, green, and blue channels (RGB), the proposed methodology allows accurate analysis of the mixing evolution irrespective of the tracer color used, while reducing the subjectivity of the estimation of mixing times by the human eye.