There are no color settings in Tools/Options/document settings for drawings that I know of.
The only way I've found to color component parts in an assembly drawing is to put each component on a separate layer and assign a color to each layer. There is a example macro in the API Help called 'Put Assembly Components in Drawing View on Different Layers Example (VB)'. I think you'll have to add the random coloring to this macro yourself (if memory serves correctly).
Ken