You can select the color correction for the picture when uploading it, you have the Original, Enhanced and don't remember the other one below the picture. If you put the "Original", I think the thumbnail is the same color as the whole picture, if that's what you mean.
@sinfulline as Thequeenzelda said: you choose the enhancement level while finalizing the upload. Choose the "Original" option to get the closest to the original color level.
@HotVR try resetting the browser cache, since CDN files might have cached for you. I see un-enhanced thumbs in your gallery right now.
@AwesomeGio that's because we've altered the upload process, and now the option you've chosen will display it correctly as described (without browser caching).