Content pulled from different sources on diff device types?

Is it possible that a different theme setting may "leak through” depending upon device type, or content pulled from a different resource depending upon what sort of device one uses to view content?

In my case, I have a rudimentary site that has an “About page.” On my desktop in the RW setup I have a black backdrop & the image dropped in at the moment is opaque. Solid black - when viewed on the desktop.

However, when viewed from the webpage, it has a dark gray cast to the theme in the body copy area.

When viewed on a small device - the image display is not identical. Image opacity may be different & there are word “fills” (the O in a word for instance & a face & hands in a drawn image which fill white vs the way it displays on desktop) which do not match th development intent - certainly don’t display the same.

Disclaimer: I haven’t investigated this properly - which should confirm or dispel my theory, but I’m tossing it up here onto the forum for discussion, in case someone has insights which have not occurred to me.