Did you read the chapter?
Shunsui says grey even though he's not wearing grey but Stark is and thats when Shunsui is able to damage Stark. Shunsui then says you have to say the color you want to cut. Stark says white and thats why he is able to attack Shunsui because Shunsui is wearing white. Shunsui then says completely contrary to your statement that the color that you choose can damage yourself as well. So far these are the rules
1. You can only damage your opponent if you call the color they are wearing.
2. The color you call can also damage yourself.
We have Shunsui=White and Stark=Grey
Shunsui then throws off his white and says Black and which point Stark is cut even though he isn't wearing Black. Theres got to be something messed up with the rules so if someone could clarify it would be appreciated.






