Yes, this part was a little tedious, but you will note that my squares are not perfect and the placement isn't perfect. I like things a little wonky, not perfect.
When all the squares were down, I carefully brushed the open areas with Soft Scrub liquid cleanser with bleach. There are more professional products made for discharging, but I had read that this works. The little scraps at the top of the picture each got a dollop as well. These were so I could test one and see how much color discharged after 10 minutes. If I wanted to leave the bleach longer, I checked another sample after 10 more minutes and so on. As it turned out, I found that after 10 minutes it really didn't change any further.
Here's how it looks after removing the freezer paper squares and washing out the Soft Scrub. Also, if you try this at home you need to treat the fabric with something that stops the action of the bleach, otherwise it will eventually rot the fabric. I use a product made for neutralizing the chlorine in aquariums called No Chlor. You can find it with pet supplies at the supermarket.
I think I may need to work with this fabric a little—add a little more color either with paint or pastels—before I really like it a lot, but thus far I am pretty happy with what I got.