Sorry to be a pain, but when I looked on my phone, the pictures I provided in my other post didn't show the issue I was having, which makes me think it's not just a Painter problem. :/
Low value colors aren't displaying properly in Painter.
The picture below is a picture of the same file open in Painter (left) and Photoshop (right).
Fixed!In color management, "Rendering Intent" was set to Perceptual. I changed it to "Relative Colorimetric" and it's fixed! Yay!