If you design a Polish tartan, you may want to look at a list of Polish flags for inspiration. I would use a lot of red and white, along with some yellow.

You might also add a dab of green or blue, but only if it looks weird without. Anyway, Wikipedia even provides the RGB colours you should use, so definitely check that out.

I am Scottish-Polish, so I'd definitely love a Polish kilt.

Regards,
Matt!