test: stricter assert color test

Make sure the assertion is actually triggered by using
`assert.throws()` instead of `try/catch`.

PR-URL: https://github.com/nodejs/node/pull/31429


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>