ale Came across this thread as I was looking for reasons why the plugin wasn't working for me. Locked layers is not the issue, as none of my layers are locked.
Am on Sketch 47.1 and upgraded to High Sierra last Friday. Opened my Sketch file this morning, to find some images washed out. Learned about the gamma correction issue, downloaded, installed and ran the plugin. Got the beachball for a few seconds, but nothing more happening. Images (only some) still appear washed out. They're images that live within symbols, but I'm guessing that should make no difference? There are other images in my file within symbols that show up fine.
Any tips on what to try to resolve this? I can manually replace them all (after which they appear no longer washed out), but would rather save myself the effort if possible.