Re: customize value hooks - be able to edit color samples in differentways...

[Richard Stallman]

    The idea was to open the Customize UI to any number of UI extensions that
    might be available now or in the future - from anywhere: internal or
    external code. If internal code will eventually provide such functionality,
    that's fine, but even then, why close the door on other possible extensions?

There's no need to spend our time on it.  People playing with such
interfaces easily redefine a function to make it call their code.
We do not need an elegant mechanism.  I don't want to spend time
thinking about it.