The color strip, as you show it, seems to have an error in it. Did it come from the STA web site? If so, I'd email Brian Wilton just to make him aware. There are some bugs in how tartans from their Index get transferred to the web site. I've discovered some tartans where the color strip is correct, but the larger image is wrong, and vice versa.

The Idaho tartan is simply a Black Watch variation. Normally if I am making a 4 yard box pleated kilt from any Black Watch variant tartan I'll pleat to whatever stripe is on the half-sett (which in the BW tartan is the black stripe on the green; for Gordon it would be the yellow line; for Lamont/Forbes the white line, etc).

However, in this case, that would be the brown stripe on the white background. If you want to pleat to show the red on blue, that can be done, but every other pleat would be different. One pleat with have the single pair of red lines, and the next would have the double pair. That could make a nice looking kilt -- there are no rules that say all the pleats must be the same! :-)

You might be able to have the kilt truly pleated to the stripe (let's say every pleat has the single pair of red lines on it), if the sett size were sufficiently small. Whether or not this is possible really has a lot to do with thread count.

We can scratch our heads and try to guess at the sett size based on the thread count recorded with the STA, but that does not necessarily have any bearing on the actual cloth. I could send that thread count in to the weavers with instructions to "weave with a 7/5" repeat," or "weave with a 12" repeat" and they would simply adjust the thread count accordingly to achieve the desired sett size.

Do you have any cloth in hand in this tartan? If you are thinking of commissioning a special weave, you can simply state the desired sett repeat.