Some time ago I inherited a piece of Holland and Sherry black pinstripe suiting material and as it was not very large, I made a pair of stubbies out of it. Today while cleaning up some of my bits and pieces I found a few of the offcuts so I did a test piece of a secured edge open seam. The fabric is very light, about super 120 but very well behaved, I overlocked the two edges with a 4 thread safety stitch then ironed the seam from both the back and the front to get it genuinely flat. The two photos below are the results.
(http://movsd.com/photos/openseam/openback.jpg)
This is the back view, it shows the overlocked edges with the seam allowance and ironed as flat as you can get it.
(http://movsd.com/photos/openseam/openfront.jpg)
This is the front view which has also been directly ironed yet there is no print through of the two secured edges.
Note that I did not bother to match the stripes properly as it does not matter in a test piece.