The DISMT ("Dual Indicator System for Mixing Time") mixing time/distance diagnostic encodes semi-quantitative visualization of liquid/liquid mixing processes in color changes. In DISMT, two liquids, one red and one blue, are mixed to produce a yellow liquid. Through appropriate choice of the acid-base indicators used, and the initial pH's of the two solutions, the yellow liquid appears only in those regions where the mixing fraction is within a designated fractional deviation (say 5%) of the infinite time mixing fraction. Thus, the 95% mixing time/distance can be defined, for the whole volume of the mixing system, as the time/distance for all of the liquid to become yellow. This paper describes: (1) the principles underlying and choices involved in the design of DISMT systems, (2) protocols for carrying out DISMT-based experiments, and (3) examples of results obtained with DISMT.