For liquid chemical products which are yellowish to reddish, color grading scales like the Gardner color scale is commonly used. The earliest form of this scale was made up of 18 standard liquid solutions, and the colored glass scale was introduced afterward to improve stability and accuracy.
Both the liquid and glass scales rely on comparing samples against the standards visually. Both methods are subjective and difficult to maintain consistent color judgment. Today, color measurement of chemicals can be done objectively and consistently using color measuring instruments like Spectrophotometer CM-5. Comes with common industrial standard color scales like Gardner color, APHA/Hazen and Iodine Color Number, and CIE Color Systems like CIE L*a*b* and L*C*h, the CM-5 provides a simple, fast and comprehensive solution to chemical color measurement.