After the sheer joy of discovering mods can be downloaded on Mac, I also discovered not all mods work how they are supposed to. Specifically, if a map or part mod doesn't support OS X (Mac), all textures show up pink. Fortunately, this only affects some mods.
Here's a list of some map and part mods without support (this is not to criticise the work of the creators), and hence have pink textures:

• Train Map
• Dunsfold
• MDA Base
• Nostalgic Simple wheel
• GridPlane 1.1
• GridPlane
• Track MVC
• Jundroo City
• Suspension test (Ground texture works, so is still usable)
• Xinshan Airport
• SP Runway Lights (pink lights)
• Death Star and Imperial Star Destroyer (technically still usable)

And here's a list of some map and part mods with support for OS X(excluding mods built with an old version of mod tools, regardless if they work or not) :

• LeMans
• Car Parts
• The Items Racetracks
• North Railway
• Monza
• The Items
• Variterra Archipelago
• Convenient Parts
• Daytona
• Nordschleife
• Camera and Display
• Hammer Airport Plugin
• Aeroclub
• Aeroclub 2
• Aeroclub 3
• Tracks
• Tracks 2
• Banks Peninsula, New Zealand
• Smoke Trails
• Smoke Trails 2
• Tracks and Roads
• SPR - Map Plugin
• Motorsport Championship
• Simple Race Tracks

I'm certain there are more mods for both lists, but the ones here are some that I know that work or don't work.

The reason I've created these lists is so that if anyone wants to look into this, they can identify features shared between mods in a list. Suspension test is notable for a working texture for the ground, but broken textures for everything else.
If anyone would to investigate this, especially anyone who knows a lot about mod, that would be smashing.