This is a boxplot where there are four subsamples of meat meal predictions. A representative of a certain batch has been divided in four subsamples and analyzed in a NIR. So we get four predictions, one for every subsamples, so the the boxplot gives an idea of the variance in the predictions for every sample based on their subsamples.
The colors are because the subsamples had been send to two different labs, so one is represented by one color. Colors had certain transparency because in some cases, two samples went to a lab and two to the other, in other cases the four subsamples went to the same lab and even in some cases three to one lab and one to another.
All these studies give an idea of the complexity of the meat meal product.