Of course one colour for each ship is enough. Thing is, that's not the only difference.
If you'll notice, even though some of my ships (especially the drones) look similar, they have different functions - mining, welding, combat, etc.

In fact, I intentionally made them look similar because I like to have a uniformity in the designs that I make. The colours are different to further signify that they are different from each other.

Are you going to spam the workshop with all of the 4,2+ billion possible colors ? Don't you think one isenough ?