A lot of pieces come in blue, but not all of them.
The focus of these contests is the appearance of the character, not replicability or purism. If someone believes Tuyet would look best with a dark blue Gahlok shield as a chest plate, they should be allowed to express that appearance.
Now, if you want to only vote for purist MOCs, that’s totally fine; I try to do that myself as well. I just don’t think it should be a mandated rule.
It’s not just about the hassle for some people; it’s also about not damaging official (and possibly retired) parts. 3d printing might be more of a hassle, but it doesn’t damage official parts.