When you see a shift in colors in your images in a Folio. The most common reason for this has has to do with the color space you selected when editing your images.
Make sure that you have selected and are using sRGB for your color space. If you have selected Adobe RGB, your images will appear to be desaturated or have a color cast.
The reason for this is that most browsers (both on computers and devices) are set up to read image files as sRGB. Even when you include a color profile, most browsers simply ignore the embedded color space information and displays them as sRGB images, leading to the colors not looking correct.
If you would like to read more about this you can check out the following articles: