Using the context menu for a specific part (or group of selected parts) you are able to customize not only the color of the part, but also assign materials (and thereby, a density) as well. When you need to control the tessellation (granularity of rendering of parts) for speed or accuracy, use this Appearance dialog also.

In a Part Studio you have the ability to customize the color of a part as a whole and also individual faces and features. You are also able to assign materials (and thereby, a density) to parts as well.

Default colors

Onshape has a predetermined color palette and rotation of color assignments as parts are created. (You are also able to assign custom colors to parts, explained below.)

As parts are created, they are rendered in a sequence of eight colors, shown below, from left to right, with the sequence starting over on the 9th part:

Default part colors

When a part is deleted, the color sequence remains intact with existing parts retaining their color:

Default part colors with one deletion