Choose 'Oxygen Yellow' it is easily seen and then follow wesoliv429's Instructions for making it Bigger. Also.... it depends on which Rendering Engine you are running. Wayland or Xorg. If Wayland it change instantly. But everything on Xorg does take a Log Out and Log back in to set it!
Further problems; don't use DuckDuckGo AI as it will tell you to Stop Being Anti-Semitic and I can't answer that. Instead don't mess around with a poor excuse for a AI Search Engine. Try Brave Browser AI as they made it more Secure, it will answer any question even if you swear. DuckDuckGo is now so full of CENSORSHIP... you can't get any answers out of it! Brave A.I. walks you through even using Command Line (CLI) Terminal to fix things and you can fix anything!