Strange color transitions in dark regions of images
Upon further investigation on color profiles after Agos's comment pointed me in the right direction, it turned out that using the incorrect color profile was responsible for the dither-like regions.

For others who have a similar issue, navigate to System Preferences > Displays > Color and select the profile that the image was exported in.

I would assume that the dithering-like region was due to the colors in that region being out of the color space of sRGB, and as a result the computer attempts to compensate.