If you are feeling fine in every other way I would try not to worry too much. I often get duo or multi-toned BM's with a mixture of light and dark
I have a man, but now I want a sheep. Man...I would really love a sheep right now. Or a pygmy goat.
Definitely don't let the two-tone get you down. It's a totally normal process. I am actually learning about what makes our poop brown in my biochemistry class right now. I figure as long as it's brown and not bright red or fluorescent green, you're probably good to go :)