The invention aims at reading, by a reading device, a 2D graphic code comprising zones including data zones encoding information based on real colours in a colour base and calibration zones presenting a predefined reference colour, the method comprising: optical acquisition of the 2D graphic code in current acquisition conditions to obtain image data, measuring of the observable colour in the calibration zones, spatial interpolation based on the observable colours in the calibration zones to estimate the theoretically observable colour for each base colour in the 2D graphic code, and classification based on the spatial interpolation for determining the real colour of analyzed data zones.