It is the simplest method and even easier than spectrophotometer. You just calibrate with black and white tiles available with the instrument and start to measure your sample by placing at a certain distance. Details are available with the instrument manual. You will receive L stands for lightness, a has two values (-a stands for green and +a for red) and also b (+ for yellow and - for blue). For greeny vegetables you will get -a and for your sample you will get L, +a and +b values.

If you have the instrument strat today and enjoy the tristimulas color values.