Strange texture effect

Some of my textures are not being read into Unity properly for some reason, in a manner that I've never come across in all the years I've been using Unity. Here's one example: the original PNG file on the left and the result when I have a shader just output the raw RGB values with no modification : the bright red becomes mostly dark red except for brighter outlines around the black spaces in the original. The same thing happens no matter what import settings I use:




This messes things up badly. Anyone have any idea what's going on?

 

[Edit: I found that the strange effect was caused by the o.Metallic setting, which darkened the main color while causing the strange outline effect around dark areas where metallic was 0. ]