What does „ICUMSA color“ mean?

The ICUMSA (International Commission for Uniform Methods of Sugar Analysis) Method Book describes a number of analytical methods (ICUMSA Method GS1/3-7, GS2/3-10, GS2/3-9) for colorimetric determination of the whiteness of sugar solutions.

The color of sugar solution is directly related to the degree of refining and used to measure the grade of quality of sugar.
The value of the absorbency index multiplied by 1000 is reported as ICUMSA Color. The resulting values are referred to as ICUMSA Units (IU) [1].

References:
[1] ICUMSA Method Book, method GS 1/3-7