Both custom clients require you to install a JDK to run them. I forget if the default does, but that doesn't matter.
If you installed a JDK you need to delete the folder from your Mac. It'll be under Java and have some sort of folder name like "JDK 1.8 etc etc etc" Just completely delete the folder.
Then go here and download this and run it:
https://support.apple.com/kb/dl1572?locale=en_USAt this point Ender's client should run and let you use your mouse. I have noticed at times the keyboard will quit working. If you restart the client this will be fixed.
Latkai's sometimes works, sometimes it doesn't boot past the updater. It's finicky to get these to work, but this should get things "playable".
The two programs to let you "change your color depth" seem to no longer do so, or this no longer works, plus they cost money. You're probably best to avoid them unless someone can chime in here verifying the process to use these and get the clients functioning because It does seem outdated info is hanging around.