Go read the defintion of Fungible then come back. It has nothing to do with tracking, tainting, marking, or subjective observations. There are no low satoshis or high satoshis or red satoshis or blue satoshis or tainted satoshis. There are only Satoshis which are ALL equal and interchangable with no difference realized on the Bitcoin network. Every transaction melts Satoshi's, not just coinjoins. Coinjoins only purpose is to obfuscate address ownership. This has nothing to do with fungibility. Don't trust me though, go look up the definition of fungible. It is not possible to identify and block any satoshis.