Install the Stylus app for Google Chrome. It can be found here
https://chrome.google.com/webstore/detail/stylus/clngdbkpkpeebahjckkjfobafhncgmne/

First go to https://www.marapets.com/online.php

Click on the S up next in the top right



click add style for: this URL



in the code box type in A:visited {color: white ! important}

You don't have to use white, you can use whatever color you want. I prefer white myself is all.

At the bottom of the box make sure it says Applies to URLs starting with (that's a drop box) and in the box next to that https://www.marapets.com/online.php





DO NOT FORGET to clear your history every day so that the colors will reset to black and you will know who you haven't visited that day.