  Privacy in block-chains is considered second to functionality, but a vital
requirement for many new applications, e.g., in the industrial environment. We
propose a novel transaction type, which enables privacy preserving trading of
independent assets on a common block-chain. This is achieved by extending the
ring confidential transaction with an additional commitment to a colour and a
publicly verifiable proof of conservation. With our coloured confidential ring
signatures, new token types can be introduced and transferred by any
participant using the same sized anonymity set as single-token privacy aware
block-chains. Thereby, our system facilitates tracking assets on an immutable
ledger without compromising the confidentiality of transactions.
