Worrying about the mainline is un-necessary, IMO.
Only when jigging with small jigs or using small bait could it be a factor, but the leader will get the effect you want. With 50 lb line from license plate flasher to fly/hootchie, who cares? Watch the video's of fish strikes....does it look as though the fish are picky? And halibut or ling cod......you gotta be kidding.
Don't waste your time even thinking about line color.....it's a non-factor.