I recently got a used Ibanez GSA 60. The guitar itself was in pretty good condition but the previous owner had really mistreated the gigbag it came with (according to him he had dumped it outside for quite a while). There is severe discoloring which looks like sun damage and in many areas it has turned into a weird "Beige" color while in other areas it's still the original dark blue.

The gigbag is heavily padded and it's REALLY good despite the discoloration. I washed it to remove some of the dirt that had accumulated and I'm looking to restore the color. The fabric is most likely nylon, judging from it's shiny appearance. Any tips on what kind of paint I can use? Will regular spray paint from a hardware store work?

You can get an idea of what the case originally looked like if you google the term "Ibanez ISGB501", sorry but I can't post links

Apologies if this is not the right subforum, I looked around and it seemed to be the most fitting category.
When it comes to painting, or refinishing a guitar or gigbag.........surface preparation is everything.

I'd try cleaning the hell out of it, let it dry thoroughly, then use naphtha and let that dry well.

Then try spray paint.

Sounds to me, like you won't make it appear any worse..............
You Dye fabric for the best results. Go to Walmart and get some black Dye and follow the instructions. It may not be perfect, but it will work the best.