The competition between the blue is increased, I think, because it's patterned/textured - I often cheat with the edge lining on an image, by sampling a tone that's already in there - especially if I want to highlight something - if you have a busy scene of boats, and only one has a red hull, and you use THAT red as the trim on your frame, guess what EVERYONE spots in that image... :-)
Cheers,
Stuart