util: add hex colors support in styleText

benchmark/util/style-text.js

@@ -7,7 +7,7 @@ const assert = require('node:assert');
 
 const bench = common.createBenchmark(main, {
   messageType: ['string', 'number', 'boolean', 'invalid'],
-  format: ['red', 'italic', 'invalid'],
+  format: ['red', 'italic', 'invalid', '#ff0000'],
   validateStream: [1, 0],
   n: [1e3],
 });

doc/api/util.md

@@ -2529,6 +2529,9 @@ added:
   - v21.7.0
   - v20.12.0
 changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/61556
+    description: Add support for hexadecimal colors.
   - version:
       - v24.2.0
       - v22.17.0
@@ -2548,7 +2551,8 @@ changes:
 -->
 
 * `format` {string | Array} A text format or an Array
-  of text formats defined in `util.inspect.colors`.
+  of text formats defined in `util.inspect.colors`, or a hex color in `#RGB`
+  or `#RRGGBB` form.
 * `text` {string} The text to to be formatted.
 * `options` {Object}
   * `validateStream` {boolean} When true, `stream` is checked to see if it can handle colors. **Default:** `true`.
@@ -2611,6 +2615,30 @@ console.log(
 
 The special format value `none` applies no additional styling to the text.
 
+In addition to predefined color names, `util.styleText()` supports hex color
+strings using ANSI TrueColor (24-bit) escape sequences. Hex colors can be
+specified in either 3-digit (`#RGB`) or 6-digit (`#RRGGBB`) format:
+
+```mjs
+import { styleText } from 'node:util';
+
+// 6-digit hex color
+console.log(styleText('#ff5733', 'Orange text'));
+
+// 3-digit hex color (shorthand)
+console.log(styleText('#f00', 'Red text'));
+```
+
+```cjs
+const { styleText } = require('node:util');
+
+// 6-digit hex color
+console.log(styleText('#ff5733', 'Orange text'));
+
+// 3-digit hex color (shorthand)
+console.log(styleText('#f00', 'Red text'));
+```
+
 The full list of formats can be found in [modifiers][].
 
 ## Class: `util.TextDecoder`

lib/util.js

@@ -36,6 +36,8 @@ const {
   ObjectSetPrototypeOf,
   ObjectValues,
   ReflectApply,
+  RegExpPrototypeExec,
+  StringPrototypeSlice,
   StringPrototypeToWellFormed,
 } = primordials;
 
@@ -45,10 +47,12 @@ const {
   codes: {
     ERR_FALSY_VALUE_REJECTION,
     ERR_INVALID_ARG_TYPE,
+    ERR_INVALID_ARG_VALUE,
     ERR_OUT_OF_RANGE,
   },
   isErrorStackTraceLimitWritable,
 } = require('internal/errors');
+const { Buffer } = require('buffer');
 const {
   format,
   formatWithOptions,
@@ -155,6 +159,51 @@ function replaceCloseCode(str, closeSeq, openSeq, keepClose) {
   return result + str.slice(lastIndex);
 }
 
+// Matches #RGB or #RRGGBB
+const hexColorRegExp = /^#(?:[0-9a-fA-F]{3}|[0-9a-fA-F]{6})$/;
+
+/**
+ * Validates whether a string is a valid hex color code.
+ * @param {string} hex The hex string to validate (e.g., '#fff' or '#ffffff')
+ * @returns {boolean} True if valid hex color, false otherwise
+ */
+function isValidHexColor(hex) {
+  return typeof hex === 'string' && RegExpPrototypeExec(hexColorRegExp, hex) !== null;
+}
+
+/**
+ * Parses a hex color string into RGB components.
+ * Supports both 3-digit (#RGB) and 6-digit (#RRGGBB) formats.
+ * @param {string} hex A valid hex color string
+ * @returns {Buffer} The RGB components
+ */
+function hexToRgb(hex) {
+  // Normalize to 6 digits
+  let hexStr;
+  if (hex.length === 4) {
+    // Expand #RGB to #RRGGBB
+    hexStr = hex[1] + hex[1] + hex[2] + hex[2] + hex[3] + hex[3];
+  } else if (hex.length === 7) {
+    hexStr = StringPrototypeSlice(hex, 1);
+  } else {
+    throw new ERR_OUT_OF_RANGE('hex', '#RGB or #RRGGBB', hex);
+  }
+
+  // TODO(araujogui): use Uint8Array.fromHex
+  return Buffer.from(hexStr, 'hex');
+}
+
+/**
+ * Generates the ANSI TrueColor (24-bit) escape sequence for a foreground color.
+ * @param {number} r Red component (0-255)
+ * @param {number} g Green component (0-255)
+ * @param {number} b Blue component (0-255)
+ * @returns {string} The ANSI escape sequence
+ */
+function rgbToAnsi24Bit(r, g, b) {
+  return `38;2;${r};${g};${b}`;
+}
+
 /**
  * @param {string | string[]} format
  * @param {string} text
@@ -204,8 +253,25 @@ function styleText(format, text, options) {
 
   for (const key of formatArray) {
     if (key === 'none') continue;
+
+    if (isValidHexColor(key)) {
+      if (skipColorize) continue;
+      const { 0: r, 1: g, 2: b } = hexToRgb(key);
+      const openSeq = kEscape + rgbToAnsi24Bit(r, g, b) + kEscapeEnd;
+      const closeSeq = kEscape + '39' + kEscapeEnd;
+      openCodes += openSeq;
+      closeCodes = closeSeq + closeCodes;
+      processedText = replaceCloseCode(processedText, closeSeq, openSeq, false);
+      continue;
+    }
+
     const style = cache[key];
     if (style === undefined) {
+      // Check if it looks like an invalid hex color (starts with #)
+      if (typeof key === 'string' && key[0] === '#') {
+        throw new ERR_INVALID_ARG_VALUE('format', key,
+                                        'must be a valid hex color (#RGB or #RRGGBB)');
+      }
       validateOneOf(key, 'format', ObjectKeys(inspect.colors));
     }
     openCodes += style.openSeq;