My PNG Sprites have Leprosy!

Hiya, friends.

Sorry for the sensational title. Anyway, I just spent an hour resizing sprites onto a custom spritesheet in Gimp, and imported my final sheet as a .png. The trouble is, when I import the sheet into Unity, the sprites are covered in splotches and weird color artifacts. On the other hand, both in Gimp and in MSPaint, this sheet looks fine; the colors are solid and the pixel edges of the sprite are clean.

Here's a side-by-side comparison of the sprites (sorry they're so small). If you zoom in on the neckline of the center sprite, you'll see what I mean:

And yeah, I'm using the point filter in the importation settings. My issue isn't that the sprites are fuzzy all around (like they would be with the bilinear filter), just that I'm getting these "splotches" of more-or-less solid colors.

Here's another example:

So, any insight on why this might be happening? I'm really baffled.