Green YouTube Videos in Safari

I have an iMac running macOS Mojave 10.14.5 with Safari version 12.1.1. The problem is that all YouTube videos viewed in Safari are green. This was also happening in Google Chrome: all YouTube videos were green. Some searching on the Internet suggested that disabling hardware acceleration would fix the problem. In Google Chrome 75.0, that can be done (Settings > Advanced > System > Use hardware acceleration when available). I disabled it, and indeed that fixed the problem. Assuming that Safari is also using hardware acceleration, I would like to try disabling it to see if that fixes the green video problem. Older versions of Safari provided a way to disable hardware acceleration, but that seems to have been removed. Is there a way to disable hardware acceleration in Safari 12.1.1?