[b]Making a custom laser sight[/b]
[u]Step I[/u] First off you have to extract the file weaponfx.pcf form your pak01dir.vpk. After that you need to open L4D2 Authroing tools and select 'l4d2 (tools mode)', when that opens select particle editor in the top left corner of the screen. (screen A)
[u]Step II[/u] now open the file weapon_fx.pcf (screen B,in red is where you should have extracted it).
[u]Step III[/u] Now you should see a bunch of effects looping on your screen, scroll down until you see the following 'weaponlasersight' and on the left menu click 'color random', then change the two colors to whatever you want(screen C) NOTE: it may appear not to change but it will have.
[u]Step IV[/u] Now you need to do the same for all files labeled 'weaponlasersight' (screen D) Afterwards click save and exit the editor,Stick the file & folders into a .vpk and put it in your addon's folder (that is where the intermediate part comes in). If you don't know how to do that then browse this site for the tutorial.
[u]Step V[/u] Launch l4d2 and make sure it is selected in your addons menu, load a game and play with your new laser sight =]
NOTE: this can be done with Weapon blur colours (red crowbar blur to blue blur) as well as pipebomb light and multiple other things.
Hope this tutorial helps and please vote.