Yellow

The Yellow is a highly modified School Bus used as a roadblock in the Lava Falls Story Mission "The Briefcase". You cannot get it through legitimate gameplay and must use cheats to drive it.

Inspiration
The Yellow resembles a Thomas FS65 Schoolbus.

Usefulness In-Game
The Yellow can take a large amount of abuse however it is very slow and sluggish and easy to hit due to it's large size. That combined with the fact it only has a single gun, unlike many other vehicles in the game makes it not viable for combat intense situations but it can still take a good beating.