Can't change image background color

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I am trying to change the image background colour to black for one of my page sections. The image I have attaches is just an example .png. Whenever I choose a transparent background image, the section background color auto changes to this blue. I've gone through the styles color editor, and even when the background colour is set to black it switched to blue whenever I have a background image added. What am I missing here?

Hi,

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