What means the yellow highlight color on the Fiddler2?
All this calls are for images and those 2 in yellow are not presented on Internet Explorer 11 (but ok on Chrome, Firefox and Edge).
Searching the Fiddler's documentation
"The default text coloring of the Session entries derives from the HTTP Status (red for errors, yellow for authentication demands)"
This says text coloring so I don't know if it is the same 'yellow', because there is no problem in authentication...