Meant to be used with the stock car instances. Mainly the benefit is losing two entities (logic_auto and the logic_switch) for each instance. Plus you can edit colors without a recompile.
To use it, remove those two entities from your car instance, and on your prop_physics car, turn off smartedit and add a key
"vscripts" with a value of "carscript", *note - do NOT type the quotes.
Save this script under scripts/vscripts
Update: 2012.06.20 I modified it to work on unnamed entities. Also note this can't work on prop_static's as they have no IO.
/*
carscript.nut
author: Lee Pumphret
https://www.leeland.info
A simple script to pick a random color when a car (or other entity) spawns
*/
/* add additional colors below */
CarColors <- [
"153 65 29",
"52 46 46",
"253 241 203",
"84 101 144",
"212 158 70",
];
local Color = RandomInt(1,CarColors.len());
//printl("Color is " + CarColors[Color-1]);
DoEntFire("!self", "Color", CarColors[Color-1],0,null,self);