In most case less color will look better (more elegance/professional) even if it only 1 or 2 difference, but since you write that you need a logo with at least 2/3 main color, so most of the participants follow that guideline.
Afterall this is your decision and your project, but if you have other competition better not put any guidelines if it is not necessary, so the participants may freely explore their idea,
We did that, exactly. All this time, thinking about how to resemble trading and automation in the logo, and design it accordingly, and when we did that, the winner comes out from a corner with none of the resemblances mentioned by them.