This paper shows a careful examination and discussion about a measurement of colour of inhomogeneous biological materials. An example of such materials is a carrot. Samples were cut into 10 mm cubes. An instrumental method for determining the changes in colour of raw, blanched and dried carrots is used in this paper. The fluidized bed drying was used as a method of food preservation. The samples which were used to drying were divided into two parts: blanched or unblanched. The drying process was carried out under specific operating conditions: 70°C and the mean of air velocity 4.5 m/s. The blanching operation was carried out for 4 minutes in boiling water. The parameters L*, a*, b* were applied to colour description. In an instrumental evaluation of colour and description of differences between the samples the following indices can be calculated and expressed in the form of: ΔE* (total colour difference), YI (313) (index of yellowness). This paper shows the influence of sample preparation on measurement of carrot colour. The results of this study show that the sample preparation is an important and significant step in colour measurement and how it could influence on interpretation of obtained experimental results. Previously to samples preparation the number of repetition was calculated. The minimum number of repetition was from 15 to 36 on the accepted error of measurement level. It depends on measurement constituents. There were observed statistical differences (p = 0,05) between measurement constituents in the following series of the same carrot cubes measurement. It was observed that the way of sample treatment had a significant influence on constituents of colour. The blanching operation of carrot cubes and further coarse grinding had a significant influence on lightness deterioration. The way of sample treatment before drying is irrelevant and not significant for lightness. Moreover the way of sample treatments (blanching, powdering) had a significant influence on parameter a*, b* and indices: ΔE*, YI313. The way of sample treatment may play an important role for further interpretation of obtained experimental results, what is shown in discussion.