"It’s customary in classical accounting to treat money as fungible, because classical accounting is expressly for the purposes of evaluating the overall situation of a business—assessing its financial health, detecting irregularities and fraud, and providing tools for auditing and verifying any claims about the overall situation by looking at whether assets and liabilities are balanced."
The problem here is that fintechs seem to want to run basic accounting software instead of banking software. These problems in banking were solved a _long_ time ago; banking wasn't the first application of computers, but they were certainly one of the first (with Bank of America having a purpose-built computer in 1959 for cheque clearing, and Barclays also in 1959 using a computer for more general purpose banking).
Banks already figured out how to solve the problems fintechs seem to be puzzled by now, and did it with first entirely paper based workflows and then later punchcard-assisted workflows for tabulation, such as "how much money does customer X have in his account?" This included things like a "local cache" of such data (for a customer with passbook savings) and dealing with all manner of fraud, and detecting that fraud without the assistance of computers.
Formance's idea here is not particularly innovative or new, and also reflects a rather common mistake when designing ledgers. A unique combination of "attribute" (which these people are calling "colours") is simply another account. This results in a somewhat undesirable proliferation of accounts.
If you use double-entry accounting and make sure your accounts are balanced and your balacing accounts are zero at the end of the day, your statements are finalised and printed and sent to your accountholders at the end of the month, your executive management refers reports of such balances each quarter, and your books independently audited each year, you will have the same results that have come from conventional banking from the days of the ancient Sumerians to the present day.
Or, y'know, fintechs could just keep inventing "new" banking models, which I guess they need to do to pretend they're doing anything more sophisticated than finding a way to juice up debit-card transaction activity at tiny banks that are allowed to charge more than big banks.