Front Panel

Here's the front right panel with six diamonds, making it about 36" long. I used two creamy whites for the neck, one is silk.

 As you can see it is much longer than most of the vests I have made. I used one size larger needle to make this happen and I could reduce the length easily by removing the last set of diamonds.

I wish you could see how the combo of creamy yarns combine to make a matte and shiny stripe.

Swatching

 I started this yesterday and by bedtime I was sure that I had veered down the wrong path. The multi-brown-gray was way too red and the variegated yarn that I used with it was too light and would draw attention to itself and would be right at your middle. So I ripped it out, and decided to keep to grays and cream at the end. 

 I have the most yarn in the darkest gray and will use that for the sides (underarms) and keep the diamonds in stripes up the fronts and back.

 I am much more confident that this will look elegant and will work for most ensembles.