Yes, if you have an sRGB profile embedded, Krita doesn't show that checkbox.

(I'm not sure I can access that file -- I get a weird kind of login screen.)

Hmm, the download link works fine for me (the "download this file" is grey so it blends a bit).

Would hate to bring up this issue again, but am having the same exact problem. In krita the color profile is set to (sRGB built-in) and the image is then exported as a .jpg file, but the entire image becomes more saturated towards red when viewed online. If the same image is loaded into GIMP and then saved with the same profile and file type it matches the correct colors when uploaded. Have read the thread but it doesn't seem like the problem has been solved, how exactly can this be fixed? D=

This is actually a problem with firefox's internal colour management, and it only happens with firefox on linux too. They fixed it in certain newer versions, but I don't know if Mint gets those, it may be they only get security updates.

But don't worry, windows and mobile phone users see your image like it should be, and so do chrome users.

You can continue saving with gimp until then if you really want to avoid the problem. Krita itself is just build around embedding colour information so it's difficult to write around this problem.

TL;DR: There's plenty of unfortunate information here, and the reason the colours look different has nothing to do with anything other than the fact that RGB is a relative colour encoding scheme.

The issue at the core is that the colour profile is mangled for whatever reason, and that it isn't being interpreted properly. In this particular case, the profile that the RGB values refer to is "Pantalla Apple Studio Display calibrado."

Untagged images are a no-no. That means that an operating system or image viewer is left to guess what colour primary lights, and their data intensity ratios, are represented in the RGB data. Apple's OSX for a number of years tagged untagged images with an unreasonable colour space, creating a very similar form of mischief.

Bottom line is that RGB is a relative colour encoding schema; it represents unique ratios of light and unique colours of each red, green, and blue data channel. Without expressing this explicitly, the actual colours in an RGB file cannot be rendered. The file in question, for whatever reason, has had a colour profile attached to it and it has, again for whatever reason but possibly ISO string reading, been mangled preventing proper colour rendering.

Colour, profiles, and many other aspects aren't nearly as complex as many artists think. Sadly, buckets of misinformation have led to a huge mess of comprehension.