Neutrals are Transformers who renounced the ideas of factions or refused to be involved in the Great War. While some resisted joining any faction by choice, others defining themselves not by faction but by world. As the war dragged on, the majority weren't suited for combat or maybe combat-suited but only for self-defense.
On the space station controlled by Starscream, most of the workers and guards onboard were neutral. However, Megatron, Brawl and Barricade have fun shooting them all into bits and imprisoning them while on their way to the Dark Energon storage area, mentioning that they're target practice to them. Most of the Neutrals were seen sporting Autobot-like colors, mostly blue with some brown and blacks, along with yellow glowy parts.