Normally I would let `eslint --fix` do this for me, but there's a bug
that causes:
const x = function ()
{
// ...
};
to become:
const x = ()
=> {
// ...
};
which ESLint thinks is a syntax error. (It probably is; I don't know
enough about the automatic semicolon insertion rules to be confident.)
The utility functions colorutils.js assume that background colors are in
CSS hex format, so require userColor to do the same, rather than
allowing inputs like "red" and "rgba(...)", to insure that inversion
checks will succeed.
