Hi William,
Yes you are completely right, the builder/yard will choose this before they have a buyer. They will normally choose standard colours and materials that a lot of people will (hopefully) like. This makes it easier to sell the yacht.
In some cases the new owner would like some things differently, in most cases this can be done. Yes, this costs time and money but it is cheaper than holding up the production process while looking for a client.
I hope this helps!
Koen
