www.makemkv.com

OK, I ripped my first UHD, and opened the resulting mkv with VLC player.

The video was all dark green. I could hear the audio just fine.

I presume the video wasn't supposed to be dark green?

Most UHDs use a different colorspace than a regular blu-ray. If you play a UHD on equipment that doesn't know what to do with larger colorspace it often looks weird. If that's what's happening in your case, you'll have to tone map the UHD into the regular blu-ray colorspace. Here's a more detailed post about colorspaces: https://forum.makemkv.com/forum/viewtopic.php?p=163176#p163176