A: There are a number of factors that affect the rendering of colours for images on your website, e.g., different browsers.
One common issue relates to the colour mode set for the original image. You might have edited and saved the image in CMYK colour mode, which is typically used for print. During the CMS upload, the mode will be converted to RGB for online display. This process might result in the colour changes you're seeing. So when designing an image for your website, make sure the colour mode is set to RGB in the first place.
Here is an article that may provide useful information.