If you don't have counter strike source installed along side G-mod, some the weapons,maps,and character models will basically just be big errors or purple and black checkered. You will need to buy Counter Strike Source to fix this problem. If you already have counter strike source then this post wont help much.
This may be a work around to having to buy css: [I haven't done it myself so I can't vouch for whether or not it would work] http://www.youtube.com/watch?v=7lkE0gmQu9w
Try this workshop addon: http://steamcommunity.com/sharedfiles/f ... =169927121 It should take care of the missing texture on the Colt. If notice any other guns with missing textures let me know.