A flow cell for measuring the color properties of a liquid flowing therethrough using interrogating radiation at a predetermined wavelength has a thin partition mounted in spaced relationship between both a window and a base of the cell. The partition and the window define an air cavity therebetween. The spacing between the partition and the window is such that evanescent coupling of radiation reflected from the liquid into the material of the window is prevented. The cell has a pressurized fluid inflow channel and a pressurized fluid outflow channel formed therein. Each of the inflow and outflow channels communicates with the air cavity. The inflow and outflow channels are sized to pass a pressurized fluid, such as pressurized air, through the air cavity such that, in use, the spaced relationship between the partition and the window is maintained by pressurized fluid in the air cavity. The pressure of the pressurized fluid in the air cavity is determined in accordance with the pressure of the liquid flowing through the cell.