Image Rendering - Colours
This occurs in rare instances and is a result of the rendering by the Shopify platform rather than the theme itself.
The theme doesn't control tone and colour of the image, only the positioning and sizing as part of the page and so on.
The best we can suggest here is to try various different filetypes, such as PNG, if you are currently using a JPEG, for example.
Other than that, it would be something which Shopify and possibly their higher tier of Support would be able to clarify and provide additional information on: