Here is the Gold Rush bomb cart, with additional skins for a red bomb and neutral bomb. The neutral cart also comes in versions with a blue light and with a red light.
To use, extract into your \team fortress 2\tf\ directory.
I have not experimented enough with the payload game system to be certain that it works with a neutral cart or with red escorting but I assume these are possible.
The spinning light on top of the cart in Gold Rush is a particle system. Valve has not released their particle editor. You'll have to use some other method to get a light effect in various colors.