This morning, I sewed all the main vertical seams on the fronts and back, trimmed the seams, ironed them and then topstitched them in a flat fell. Probably more ironing than sewing but still, a fair bit of both.
The light in this photo makes the green look unfortunate and not at all like the bright, cheerful colour it is, but that shows up later. You can see the back, two fronts and the bottoms of the two sleeves, plus tabs and pocket flaps. I can see (close up) that I have used slightly different shades of green for the main seam stitching but I did make an effort to use the matching green thread for the top stitching. Then I filled a bobbin with the blue and did the top stitching of the contrast pieces.
First however, I pressed the heck out of the seams on the contrast pieces. I pressed the seam open on the wrong side.
Then I made sure it was really flat on the right side. Then I pressed the edge together so that the blue was on one side and the green on the other. If I hadn't done all that initial pressing, I might have had bits of the fabric rolling into the seam ditch and it could have been a mess. This way, it's neater and frankly, easier even if it does seem to take extra long in the pressing department.
This is an extreme close-up of the edge of the collar. You can see that on the underside (the blue side), you can just see a bit of the green. However, on the up side (the green side), you can't see the blue. I won't be wearing my collar turned up like they did in the 80s (or was that the 70s?) so I made sure the blue wouldn't be seen at the edge of the collar when it was lying flat. I suppose it doesn't matter but I had to decide one way or the other and this is the way I went.
Here is a close-up of the topstitching. I used blue for the bobbin thread and green for the top. In this photo, you can also see the difference between the right and wrong sides of the fabric itself as shown on the sleeve to the right of the pocket flaps.