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The mixing process is a multivariable and intrinsically non-linear plant. Mathematical modelling of the mixing color process has been taken into consideration in order to design an adequate control (PI controllers) to assure zero steady state, fast control and disturbance rejection. The comparisons of the nonlinear mathematical model and linear one have been done. The control of the process has been implemented by using STEP7 Programming Software for Siemens SIMATIC Programmable Logic Controller (PLC). The entire process has been implemented in Matlab-Simulink environment. The process control has in view maintaining an appropriate level of liquid and a color as close to that required in the mixed tank, and only height control in auxiliaries tanks. Controlled process has been implemented on-line using specific language for Step7 (FBD - functional block diagram). Additionally, in order to use in industry by an operator for the implemented control has been created a friendly and intuitively HMI (human machine interface) in WinCC.