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Do any other colors, of any element, or any picture, on your FujiFilm camera's screen, show a different color or differing shade?
I'm doing a brief bit of research on that set of symptoms... I seem to recollect something similar...
On one camera - admittedly not your model - the focus square becomes yellow if you are in Manual Focus mode.
Is there any chance that you have switched out of Autofocus (in which the focus square - at least on another Fuji camera than yours - is not yellow, but becomes yellow in Manual Mode...) ?
I suggest, if the former advice is not useful, that you might want to try doing a factory settings reset of your camera, and see if that clears up the problem - as well as checking all the exterior switches on it for correct settings.
In other words, no change?
Has there been no change after a reset?
Or do you mean to ask, Is the yellow square color normal? NO, not if you noticed it was another color previously!