`styleText()` doesn't work within a worker thread

Version

26.8.1

Platform

Darwin MacBook-Pro-de-Sebastien.local 24.6.0 Darwin Kernel Version 24.6.0: Tue Apr 21 20:16:56 PDT 2026; root:xnu-11417.140.69.710.16~1/RELEASE_ARM64_T6030 arm64

Subsystem

No response

What steps will reproduce the bug?

const {Worker} = require('node:worker_threads');
const {styleText} = require('node:util');
const tty = require('node:tty');

console.log('MAIN', {
  isTTY: process.stdout.isTTY,
  isatty: tty.isatty(1),
  styled: JSON.stringify(styleText('red', 'hello')),
});

await new Promise((resolve, reject) => {
  const worker = new Worker(`
    const {parentPort} = require('node:worker_threads');
    const {styleText} = require('node:util');
    const tty = require('node:tty');

    parentPort.postMessage({
      isTTY: process.stdout.isTTY,
      isatty: tty.isatty(1),
      styled: JSON.stringify(styleText('red', 'hello')),
    });
  `, {eval: true});

  worker.on('message', msg => {
    console.log('WORKER', msg);
    resolve();
  });

  worker.on('error', reject);
});

Output:

MAIN {
  isTTY: true,
  isatty: true,
  styled: '"\\u001b[31mhello\\u001b[39m"'
}

WORKER {
  isTTY: undefined,
  isatty: true,
  styled: '"hello"'
}

---

Even simpler repro:

const { Worker } = require('node:worker_threads');
const { styleText } = require('node:util');

console.log('main:', styleText('red', 'hello'));

new Worker(`
  const { styleText } = require('node:util');

  console.log('worker:', styleText('red', 'hello'));
`, { eval: true });

How often does it reproduce? Is there a required condition?

constantly

What is the expected behavior? Why is that the expected behavior?

I think it's reasonable to expect styleText() to also work in worker threads by default if the parent has colors enabled. I'd rather have an opt-out than an opt-in through worker thread config/env.

What do you see instead?

The worker thread

Additional information

From what I understand, the heuristic used in styleText() is too limited and could be improved to support colors in worker threads better

• https://github.com/nodejs/node/blob/main/lib/util.js
• https://github.com/nodejs/node/blob/main/lib/internal/util/colors.js

In chalk, this works out of the box, based on https://github.com/chalk/supports-color

Reproduce the worker_threads example first, then inspect lib/util.js and lib/internal/util/colors.js, which the report identifies as the relevant heuristic. Compare color detection in the main thread and worker, and consider the parent-process color setting described in the expected behavior. Done means styleText() produces the expected colored output in a worker when colors are enabled by the parent.