Brake cleaner sometimes works on tough stains too. just have to very careful and clean with a regular cleaner right after you use it, but it will take out some tough stains.

I had A bird poop stain on my upholstery and had the same problem, but mine was on yellow upholstery. I ended up using a Clorox Bleach Pen. I had to leave the pasty solution on the stain let it alone to dry, and wipe it off a day or to later after sitting in the sun. I thought Bleached yellow would be better than poop stained yellow. However it did not discolor at all, and came clean! I still use that now, when I get spider poop on there and it leaves a red stain that will not come off with regular cleaners. I would try it in a non visible spot to make sure but, hopefully the bleach will work and not die the color.