Does the coloured coins spec (or an informal convention amongst its implementers) track coloured coins left to the miner of a transaction's block in the standard manner?

Obviously the miner would have to be running a coloured-coin-friendly mining implementation, but I was wondering if anyone knows whether there is intended to be a way for a coloured-coin-recognising miner to do this.

The coloured coin spec document at


Makes no mention of mining except to say that

Fee[s] should be paid using uncolored coins. If it is absolutely necessary to pay [a] fee with colored coins, that color should go...last.

Is it intended that in this scenario the miner can "collect" the coins while retaining their colour?

2 Answers 2


Although the standard way of dealing with colored coins left for fees is to uncolor them, it is possible to offer colored fees.

This has been recently discussed in the bitcoinx mailing list. I quote Alex Mizrahi (Killerstorm) for an explanation on how to do it:

"Pay a small amount of colored coins to output OP_TRUE script. Anybody can spend it, but usually that would be miner who mines next block and can recognize OP_TRUE script. Thus miner can construct transaction which pays colored coins to himself and include both into block he mines."

This is the original thread: https://groups.google.com/d/topic/bitcoinx/JshJboR_vWc/discussion

  • Ingenious! I forgot about OP_TRUE. Currently this would require a custom-built client to build the transaction manually, correct? Commented May 4, 2013 at 16:10
  • It would require a specialized color kernel implementation (or a modification of the existing ones)
    – jtimon
    Commented Jan 14, 2015 at 13:03

Although it's not covered by the specification, it seems logical to match all transaction fees (in the order in which the transactions appear in the block) against the block reward the same way other transactions are matched. The leaves only whether the block reward comes before or after the transaction fees. I think it makes the most sense to put the block reward after the transaction fees, since the block reward will always consist of uncolored coins (unless someone "pre-colors" them, which seems strange), and the convention is that uncolored coins go last.

  • I agree, but is this actually being done in any implementation of the coloured coin concept? Commented May 4, 2013 at 9:00

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.