That's quite awesome. Armenian cukes can either be light or dark, depending on the variety. But not half and half.

Now there are bicolor squash (e.g. Zephyr, a pepo), but the two ends are different colors in that case. Half green and half yellow.

Can you harvest the seeds to see if any of the offspring would share this trait?

That is very strange! I’ve grown Muncher for many years — definitely my favorite cucumber — and mine have never done anything like that. :O)