Painting is definitely a procedure that truly distinguishes the model from the toy, because here is where expression is transformed from gray plastic or bare metal, into vivid and captivating imagery.
In choosing the paint scheme for your army, you can reflect on its identity. If your army is secretive or stealthy, then a dark color such as black or a dark red can reflect this. You can buy citadel paints via online sources.
If your army is composed of noble and selfless heroes, striving for the common good, then a bright color such as white, or a regal color such as navy blue can reflect. You also do not need the army will be limited to a set color scheme.
Many of the races found in the Warhammer and Warhammer 40K has a unit, which allows for a different color scheme, marking them as Special Forces. Some races have a background, which also pushed the color varies; Knights Bretonnian example, tend to have a very personal symbol, which means that even in a single unit, there is unrest contrast.
In Warhammer 40K individual soldiers as Death Company of the Blood Angels, or Eldar Aspect Warriors have a color scheme, which distinguishes them from the rest of the army. In the end, the only limit on your army composition, shape, and color, is your own imagination.