Why is color the least reliable method for mineral identification?

Colour is least reliable property to recognise mineral in field. but is best for studying and recognising mineral in lab under Polarized light microscope (PLM). <br /> let us take a simple example of quartz and calcite both have nearly same colour range so just by observing colour you can not give a guess but by applying different field techniques at same time we can distinguish them as calcite can be scratched by nail but quartz will not be scratched. <br /><br /> (Allah Knows the Best) <br /><br /> One interesting thing is that colour is most deceiving thing in this world. About 90% of frauds are done by colours. it I think I need not to explain it. :-) <br /><br /> CHEERS