I would like to ask why the absorbance of cyan light of the testing solution ( with ethanol ,distilled water and beetroot) increases as the ethanol concentration increases from 0% to 75% but drops as the ethanol concentration increases from 75% to 100%??
Also, when the ethanol concentration increases from 50% to 75% , the reading of colorimeter has fluctuation?
Fluctuations are normal with colorimeters - I'm surprised you only had it at 50-75%. I would expect the reading to level out rather than fall between 75-100%. The 'drop' could be due to normal experimental error/variation, or may be due to some sort of chemical reaction between ethanol and the pigment, causing it to change and become less 'colourful'.