A stated rule needs annotated exceptions

"No hardcoded whites on semantic surfaces" is a good rule with real exceptions: a control floating over a photo or a video legitimately stays white. That combination — enforceable, but not absolutely — is the one that decays, because after a few months nobody can tell which of the remaining hardcoded colours were decisions.

The fix is cheap and mechanical: state the rule where it is established, write one line of reason where it is broken, and keep a command that lists both.

Traps

A rule you cannot grep for will not be enforced. "No hardcoded whites on semantic surfaces" is enforceable because the violation is a literal token. "Use semantic colours" is not, because the compliant form is the absence of something. Write rules in terms of what appears in the file.

The reason belongs at the call site, on the line above. A file-header note saying "the whites in this file are all over video" is true on the day it is written and false the first time somebody adds a block below. It also cannot be read at the point where the reviewer is looking.