GB/T 2379-2020 "Acid Complex Dyes—Determination of Shade and Strength" is applicable to the determination of related properties of acid complex dyes. It specifies two testing methods: the dyeing method and the solution colorimetric method. The dyeing method can be performed on wool or nylon fabrics, where dye solutions are prepared according to specific formulations, with control over the corresponding dyeing temperature, bath ratio, and holding time. The test sample and the standard sample are dyed under the same conditions. The solution colorimetric method is conducted through instrument detection. Shade and strength can be evaluated by visual inspection or using colorimeters and spectrophotometers, with results determined by comparison to the standard sample. The standard specifies requirements for reagents and instruments as well as operational procedures to ensure consistency in testing.