I've tried using every format in the book, from PNG to JPG(ugh). No matter how I save it, the colors goes from looking great in Paint.net to much less vibrant and bland when uploaded to the internet. Here's an example. The image at the bottom was taken from Reddit and resized and reuploaded to imgur as a PNG. The resulting image is shown at the top left. (The image to the top right is unrelated).
I used the search feature here, and checked the 'common problems and solutions thread' and was unable to find anything. Any help would be appreciated, thanks!