Sorry to hear you are concerned about the darker portion of your foreskin. Don't do anything crazy to change it and end up damaging your nice feature. I think it might be a distinctive part of your penis, and you should take pride in it. Part of the reason for the darker color is probably because in the flaccid condition the end foreskin is compressed more, so the color is more concentrated than the other part on your shaft.
I'm German heritage and could be considered "fair skinned" too, but I get out in the sun regularly to get some color, and when I can, I sunbathe naked to get a full body tan. My penis shaft really takes the sun and gets pigmented deeply. My cock is now darker than the rest of me, and I love it. Like brown eggs...brown cocks look healthy.