You basically give me an order what 30x50 flag do you want, it can be any 30x50 flag you can imagine, just say the appearance of it and the colors and it will be done.
Is that a good enough description? Don't know if that will work.
I thought diagonal is from one corner to another, you could say 3 lines that go from top to bottom, angled by 15 degrees on the left...with blue on the middle of each of them