You will need to install a user script manager extension to install this script.
Simple theme changer for youtube with some tweaks. By default changes youtube red color to slightly neutral one and allows videos to take up whole window in wide mode. (Also clears some ads)
Adds mousewheel volume adjustment functionality when hovering over video.
Script has 3 console commands:
pickcustomcolor(); - opens color picker to let you choose theme
setcustomcolor(/*color in hex rgba or hsl*/); - sets theme from string you provide
resetcustomcolor(); - resets to script default neutral red