I recently brewed a AG Kolsch. At bottling time, I split it into two mini-kegs, force carbing the first, and putting a co2 blanket on the other and set it aside for about a month. The first was a nice light tasting classic fizzy yellow beer, with decent clarity. I just tapped the second one today, and found a light-red grapefruit color. The beer tastes the same although I need to carb it up a little more, but the color is very different. What could cause this?