The selection of pigment carbon black is based on the coloring characteristics or physical properties, with the choice of the type of carbon black for coloring primarily determined by the required darkness of the finished product. Very fine pigment carbon black can achieve a high darkness level for coloring; for products like PE garbage bags, plastic bags, and cable materials, a moderate darkness level is sufficient and can be achieved with carbon black varieties that have a lower specific surface area and a higher structure. Microscopic errors in the measurement and blending of carbon black during plastic coloring can lead to significant color discrepancies, so it's advisable to use low-pigment carbon black with larger particle sizes and lower coloring power. This allows for a slightly higher carbon black dosage with relatively smaller measurement errors, and also offers the advantages of better dispersibility and lower cost. For gray plastics, fine-grained pigment carbon black often results in a brownish gray, while coarse-grained pigment carbon black can produce a bluish gray.