hackernews.user.js

// ==UserScript==
// @name         Hacker News highlighter
// @namespace    http://tampermonkey.net/
// @version      0.2
// @description  none
// @author       lpimem
// @match        https://news.ycombinator.com/*
// @grant        none
// ==/UserScript==

(function() {
    'use strict';

+ function () {
  function color(sp, c) {
      let r1 = sp.parentElement.parentElement.parentElement;
      let r2 = r1.previousElementSibling;
      [r1, r2].forEach((v)=>{
        v.style.backgroundColor = c;
      });
  };

  function highlight(score, sp) {
    if (score < 100) {
      return;
    }
    if (score < 200) {
      color(sp, '#DFD');
    } else if (score < 500) {
      color(sp, '#DFF');
    } else if (score < 1000) {
      color(sp, '#FDD');
    } else {
      color(sp, '#F99');
    }
  };
  let scores = document.getElementsByClassName("score");
  for (let i = 0; i < scores.length; i++) {
    let score = Number(/(\d+).*/.exec(scores[i].innerText)[1]);
    highlight(score, scores[i]);
  };
  return null;
}();
  
})();

Install for Greasemonkey or Tampermonkey