Purple Checkerboard on maps.

Hi, I bought Gmod a few days ago and began downloading a couple of third-party material for it. I’ve been noticing on a lot of maps I’m seeing purple checkerboards and tall red errors standing around. I suspect I’m missing some content of some sort, so my question to you is, what addons are essential for many gmod maps to work? I have wiremod and Phx3, but that’s it.

That shows up if you are missing textures. Do you have Counter Strike Source?

Purple checkers are missing games (Most often).
Red errors are missing mods. Ask the people in the server what they are, then go download it.
Also: http://www.facepunch.com/showthread.php?t=688324

Purple checkers are missing textures, you are probably missing htem because you don’t have a specific game or a texture pack for a map.
Red erros means missing models, you need a game or a model pack for a specific map
what games do you have?