A microfluidic, vision-based pressure sensor is tested with three different concentrations of coloured solution, which serves as sensing fluid for the sensor. The sensor is based on the deformation of the a polymeric chamber, which causes the sensing fluid to flow in or out of the sensing area, resulting in a change of colour intensity. That change is recorded by a digital camera and the average darkness of the sensing area is calculated from each frame. Pressure and darkness value are highly correlated, with an absolute correlation of 0.9293 or higher. Thus, for each colour concentration a linear transfer function is determined. The different concentrations greatly differ by the correlation factor, which is defined as the slope on its darkness-pressure plot. The 30% solution's correlation factor is about 3 times lower than the 5% solution's factor, resulting in a 3 times finer resolution of 2.2 kPa on average.