The colour of oils and fats is mostly due to the presence of colour compounds such as carotene and chlorophyll. But some colours also develop during storage, heating etc which are due to oxidation. The colour of an oil and how it behaves during processing is therefore an important indication of its quality and oil trade specifications give maximum limits. There are many different systems for measuring colour, but for oils and fats the usual instrument employed is the Lovibond colorimeter which reads in red and yellow units. The red colour is by far the most important. Users prefer oils to be as pale as possible and so the colour is removed, as far as possible, in a process called bleaching. Oils which are difficult to bleach not only require more bleaching treatment, but also have poorer shelf life. The usual colour specification for good quality RBD PO,olein and stearin is 3 Red, while for CNO and PKO is 1.5 Red, all in 5 1/4 inch Lovibond cell.