Chocolate pods from same plant as red ones

Hi all

I'm relatively new to growing peppers, and have been growing a few varieties of peppers indoors since last fall (poblano, jalapeño, tai chilies, orange habanero and ghosts) and have something I at least consider odd....

My poblano plant has been producing "normal" coloured pods for over a year now, and last week had one that ripened to dark brown (chocolate?) all others ripen red as I would expect.

Is this a normal occurrence that every once in a while a plant would throw a different colour pepper?

Chocolate poblano? I'm no pepper pro but never heard of that before. Although, that is how other varieties came about, natural mutations of some sort or another. Save the seeds and plant them, see what happens. 
I grow ancho mulattos - a poblano type that ripens first to chocolate brown then to a reddish brown. If you haven't picked it yet, wait and see if it changes further. 
Something worthwhile to think about - green and red are complimentary colors - they are opposite each other on the color wheel. If you paint (or draw with pastels or colored pencils), you know that mixing complimentary colors usually ends up with a muddy grey-brown color (sometimes referred to as "mouse grey".) Chiles that ripen from green to red might well display as brown as an in-between color for the same reason.