This is the post that I wanted to find a few months ago when I discovered bleach had gotten onto Rez's $40 scout uniform pants. I didn't want to buy another pair, they were not that old and in really good shape otherwise. The bleach turns the green a lovely lavender color.
They are made of some microfiber fabric, really nice but not easily dyeable. I looked up how to dye polyester, not an easy proposition and that is assuming you can find the right color of dye.
So, I came up with my own solution, fabric paint.
I mixed these 4 colors to get a color that was close, then dapped it on to the bleach spots, rubbed it in and let it dry.
After a day or so, I washed them.
It turned out pretty good, not perfect, but when you look at them you think more of camouflage than, "my what a lovely lavender that is."
I ended up buying another pair of pants for "dress", but these work great for when he is on hikes, etc.