Two pressing tricks. Both are based on the idea that the fabric really takes a set when it is heated, then COOLED in the desired position:

1. If you have two irons (or have an ingot of lead or other metal you can handle -- get creative here!), use the heated iron to press an area. Then place the unheated iron, or ingot, or what's called a "sad iron" (Google it) on the area to pull some of the heat out quickly. Keep moving along, hot pressing then cooling each area in turn.

2. If you can spare the area, shortly after pressing (while fabric is still warm), cover it with a protective cloth, piece of posterboard, whatever. Then weight it down with books, bricks, what-have-you and leave it overnight. Be careful that you aren't pressing in unwanted wrinkles! This works best while pleats are still basted, but if you're careful you can still lay out the flat part of pleated area (below the fell) and weight it down smoothly.

Again, both ideas allow the fabric to cool while being pressed into the pleated position. Hairdressers use the same concept to "set" curls in hair. It probably has more effect on hair, wool, and other natural fibers, but your mystery fabric can't help but be impressed by the effort as well

And, oh yes, great colors!