Actually, they caught the exchange that created the purple ligtsaber on film. Sam was not at all as bratty as y'all are making him out to be. The exchange went almost exactly like this:

GL: So, what do you want your lightsaber color to be?
SLJ: What colors you got?
GL: Good guys are blue and green. Bad guys are red.
*pause*
SLJ: How about purple?
*pause*
GL: Okay.

That hardly seems like mollycoddling to me. That said, the aesthetic value of a purple lightsaber sells for a loss, if you catch my drift.