Fifty shades of banking regulation might not sound very titillating. Perhaps it should be.

A new Federal Reserve working paper lays bare the degree to which ostensibly black-and-white rules set by the Basel Committee on Banking Supervision differ in their implementation.

At issue is the way in which countries can enforce requirements under Basel bank capital adequacy standards first introduced in 1988 and subsequently updated in 2004 (Basel II) and then overhauled in the aftermath of the financial crisis in 2010 (Basel III). While such rules set a minimum required capital level for banks, countries retain leeway in calculating the ratio by which that level is achieved — allowing for tinkering in the numerator (definition of capital) and the denominator (risk-weighted assets).