Re: custom type `color' is not enforced

[Richard Stallman]

    Don't assume that the user knows just which option s?he wants to describe.
    `describe-variable' gives you only one way, by option name, to define a set
    of candidate options, in order to pick one to describe.

I'm not assuming that.  Rather, I don't think very many people
would take the trouble to remember that `describe-option-of-type'
exists.  Thus, practically speaking it would not be very useful.