It can sometimes be useful to design in colour, especially when you need to highlight a change in the structure or a separate set of components.
Colour can be used to highlight specific elements, such as walls or floors, or it can be used to highlight whole areas of the building, such as a new extension. Colour can also be used to accentuate different levels, types of wall-object and components of non-structural systems eg plumbing.
It is becoming more common for Planning/Permit authorities to request that new Works are indicated in colour; this should be confirmed with your local authority. Where applicable, it is recommended that you add a light colour shade to your drawings. Where colour is not a requirement, the authorities rarely reject drawings with colour features as long as the colour is used with restraint and to enhance understanding.
The use of colour in Sketchup is explained in Chapter 9 of the Nested Matrix book.