The authentic one is yellowish brown. Some manufacturers will dye it to mimic the color of Dong'a Colla Corii Asini blocks. But you only need to see whether the section is flat, whether the light is translucent, whether the smell of glue, whether a break that can be determined whether it is a good gum. If it is, it is definitely a good Colla Corii Asini. A little more in-depth is to put in a bowl steamed, stinking is the garbage gum, many small factories will use chemical reagents coloring and flavoring.