something wrong happens when Unity packs the provided desktop icons (16,32,48,128,256,512,1024) into a single .icns bundle.
Once packed, OSX Maverick shows corruption in color data at certain size.
In this example I see corruption in 16x16 size, the other sizes show up correctly.
The problem seems to show up randomly. By changing the images I came up with the same problem on 32x32 and 48x48.
I actually found another thread that said to switch the texture to True Color, which fixed the error in my case along with making sure that “Alpha from Transparency” was selected. The texture was a 512x512 PNG, and when it was set to compressed, the 128 icon would be corrupt but the rest of them (including the upscaled 1024 version) were fine.