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Every refinery/sugar factory has a challenge to deliver sugar within the specifications, while averting excessive wash of the crystals. Wash is needed to clean the crystals of the surface film of mother liquor containing ash and colorants, however, excessive wash dissolves good product. Dissolved sucrose sent back in the process for renewed crystallisation requires costly extra capacity, water, and energy. To avoid exceeding the highest sugar colour allowed for sugar going to the bin/silo, it is necessary to work with a safety margin to the target colour set for the daily operation. This paper will discuss how different methods for colour measurement influence the size of the safety margin. After a short overview of different methods, application of the ICUMSA "General Guidelines for Validating Indirect Technologies" will be described. These guidelines may be applied to any kind of indirect measuring technology. The focus will then be on discussing the safety margin for the ICUMSA methods for solution colour and for a real-time method measuring wet or dry crystals online, directly in the production. Further, practical examples of reduced safety margin will be given. [ABSTRACT FROM AUTHOR]