In the link provided, it suggest searching for 'Materials', but that isn't the best choice...
SU should have two Material folders but only makes the 'User' one when you make a new material inside SU...
so it better to look for a redundent [still included] folder that has always been placed in the User path...
to open it in Finder you can copy/paste into Ruby Console...
`open "#{Sketchup.find_support_file('OldColors')}"`
on mine that's /Users/johns_iMac/Library/Application Support/SketchUp 2016/SketchUp/OldColors
In that SketchUp folder add a new folder named Materials [it will not get deleted on upgrading]...
add any material sub-folders into there, they must contain skm files to work...
once made drag it into the Finder sidebar for easy access
[image: TKpz_mac_mats.gif]
there are other gif mini tuts about add materials from inside SU...
john