Of the 3 choices you have asked about I like the dark green the best. If you do the setting triangles in say the dark green, then do sashing w/ corner stones, keeping the corner stones the same color as the setting triangles and the sashing a contrasting color it will look like you have alternated the octos w/ a churn dash (or monkey wrench) type block. I have seen it done w/ other octos and it looks great.