With my most recent picture (Cheek Kiss Series: Gabby and Spike), I've noticed that the colors are a little washed out here, but more bright and vibrant on DeviantArt.
I uploaded the same file to both sites. Not sure why this is happening, but at least I'm fairly sure it isn't Clip Studio Paint this time.
Update: From what I've seen so far, proper colors appear on Deviantart and Furaffinity. Muted colors appear here and on Baraag. Those are all the sites I upload to. What makes this frustrating is that different sites allow different content, so I won't always be able to just link to somewhere else.
Update 2: Fixed it finally. Sort of a combination of things I tried before. Apparently, I have to export the final picture using Photoshop, not Clip Studio Paint (which you might recall I tried before with no success). I think the reason it didn't work last time is because I had to change the color profile in Clip Studio Paint first, THEN open the file in Photoshop before exporting it. I have no idea why a jpg would look different on Inkbunny compared to Furaffinity just because I used a different program to export it (on my computer, the jpg exported from CSP looks the same as a jpg exported from Photoshop). In any case, it looks like the problem is finally solved.
