Blue, no doubt.
Knowing that your sacs hold a load that could knock a can of Pepsi onto its side, or damage a passer-by's eyes slightly, it's both reassuring and empowering.
Plus, the cock looks better when the balls start to change their hue to blue, it develops this fine, waxy, healthy sheen.
Much better than a wanked-out, shredded cock that barely squirts tears when yanked to completion. :thumbsup: