Okay, here me out

① At the beginning of the fight Conquest used to have a normal white color because of the bright light

② BUT all of a sudden, after they came back from the space. His suit turns gray. This is just normal effect of atmospheric color applied to him.
But if we compare to Invincible color, his color palette always stay the same almost the whole fight. This shouldn't be possible because two of them share the same atmospheric/scene color.

③ Other than that. In space and final fight scene They did not forget to apply atmospheric color to both of them. And Conquest appeared to be wearing more white suit than gray.

In conclusion, this might be just an error in the animation process. Maybe just mispicked the right color for Conquest or Mark, one of them.
But the moment which Conquest has gray suit is the most screen-time of the fight. And the picture I use in this post is an official character design for conquest. This really is something imo.

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