Can't apply MBG skins for marble

I can't figure out how to implement downloaded skins or levels. I'm on a mac and I've tried placing them in their respective folders but nothing has worked

In order to use custom marble skins in MBG, you'll have to install a marble selector.

An easier method is to replace the base marble texture with the one you'd like to use, but it must be changed manually.

Are you installing the levels to the game files in your Library folder, or the files in your MBG app?

I've tried many times to replace the base skin but nothing I've done has worked, while doing the same to skyboxes and other graphics has worked. How do I download a marble selector?

Try replace the original one with the one you downloaded. If the downloaded one is in JPG, name it "base.marble.jpg". Then create a pure black image that's the same dimensions as those of the downloaded marble skin and name that one "base.marble.alpha.jpg"

eNetro is correct. I would recommend just trying that.

However, if you're still interested, here's the link to the guide for the marble skin selector:

github.com/PlatinumTeam/MarbleSkinSelection

The old version of this worked on Mac, so I have no doubts that it still does.

Got it all figured out, thanks for the help!