Trying to remote desktop into an Apple

The short answer is yes, you can do it from an Ubuntu session using Remmina. I have set one up and it is working fine. I do have mine hardwired to my network, and my connection opens at the Poor (fastest) quality connection.

In the screenshot below, you can see how I have my MacBook setup for Screen Sharing.

Then in Remmina, I set it to VNC, put in the IP address of my MacBook Pro and clicked Quick Connect.

Then typed in my short username from the Mac and my password, and it is stable and working fine. The top screenshot is actually from my Remmina session connected to my Mac.

Also make sure to set the color depth to greater than 8bpp in the profile if you create one:

If yours is set this way, and still having problems, you might want to try removing and reinstalling Remmina.

Hope this helps!