Since the gentleman wears BDU pants for work anyway, he ordered a pair in dark blue as a base to start from. They were a little light, so I dyed them darker, then took off the cargo pockets, so I could add the white stripes. This is where I very much appreciate heavy fabric in general, and ripstop in particular - once you get a seam partly unraveled, you can just rip the two pieces apart, knowing the seam will go and not the fabric itself.
It took some doing to find white ripstop material, since most people want ripstop for tough wearing, which is not really synonymous with situations where white would be useful. I did eventually find a reputable website that had it though, and ordered the 2 yard minimum. Turns out it's good I overordered, because one layer of it against the dark blue looked kind of dingy. Two layers, though, looked pretty decent, so I cut out basic shapes to the gentleman's dimensions and sewed them on.