Makes the chat username colour the same colour as the chat text. Supports both light and dark modes.

Twitch Plain Chat colours.user.js

// ==UserScript==
// @name         Twitch Plain Chat colours
// @namespace    https://techygrrrl.stream
// @version      0.1
// @description  Make the chat username colour the main text colour.
// @author       techygrrrl
// @match        https://*.twitch.com/*
// @match        https://*.twitch.tv/*
// @grant        none
// ==/UserScript==

(function() {
  'use strict';
  
  let found = false

  // Check and click in milliseconds
  const CHECK_INTERVAL = 200

  setInterval(() => {
    perform()
  }, CHECK_INTERVAL)
  
  function perform() {
    if (found) return

    const css = `
      .chat-author__display-name {
        color: inherit !important;
      }
    `

    const styleTag = document.createElement('style')
    styleTag.innerHTML = css

    document.head.appendChild(styleTag)
    
    found = true
  }
})();