How does LEGO decide the color of internal set pieces? While building many LEGO sets I have noticed that for internal pieces you cannot see when the set is finished; LEGO often chooses mis-matching colors.  For instance in the (amazing) Saturn 5 set most of the pieces are of the white, black, gray family.  However there are some green/blue internal pieces.  Doesn't match the rocket at all.  I have noticed the same thing with other sets as well where a random green internal pieces will show up.

Do they do this for a reason?  Are they using colors that don't sell well and trying to get rid of them?  Going for contrast to help you build?
Going for contrast to help you build?


This is probably the primary reason most of the time.

One Eurobricks user once said they asked a set designer about it, and they confirmed they do it to makes it easier to follow the instructions:


  I had an opportunity some time ago to talk to a designer at TLG, and he told me that they use other colors to make it easier to follow the instructions and build the model.