Color mixing is the process of developing new colors by using the combination of two or more primary colors. Most oil/water-based paint users usually depend on the visual observation of the paint mixture based of the past experience to ensure the expected color is got mixing by try and error. This practice leads to inconsistency in paint quality, difference in color and less homogenous. Now a days there are modern mixing machines which ranges its costs from $1500 to $2500 which is not affordable for low level end users. In this study a simple, low cost and good handling system machine was designed and implemented with 2-liter capacity. Data feeding system is taken place by phone application as graphical user interface (GUI) designed on MIT app inventor with two display pages i.e. the first page includes data input boxes, mix display box and ‘ገጽ2’ option to jump to the second parts for the color sensor result display labels, the fed RGB& total volume values for comparison and CMYK values with their corresponding volumes to be mixed for the given input data. Since CMYK color model is subtracting type of color mixing system, Cyan, Magenta, Yellow and Key (black) colors were to be mixed together with white to subtract white color. Experimental investigations had been taken place taking different inputs and the results were evaluated carefully. The machine performance was characterized and cost effectiveness was determined. The overall performance of the prototype was 94.5%. Generally, the study demonstrated the possibility of producing an affordable automatic paint mixing machine with good performance for low level traders and manufacturing shops. The machine has simple and accurate data feed system, easy mixing algorithm and mix color feedback system and very flexible for any paint type and power supply source change (i.e. the power supply could be 12 V DC battery charged with solar power if there is no any electric power around). Keywords: RGB, Paint Color Mixer, CMYK, graphical user interface (GUI)