Beyond Compare will mark some parts blue. Beyond Compare is trying to tell you "these are different, technically, but you probably won't care".
Uppercase and lowercase are considered unimportant differences.
The real information about what is different between File A and File B is in the color of the letters. Letters change color to show file differences. The yellow letters are different in the files above, the beige letters are the same. (Note about my color settings.)
Background gives a summary of the entire line. Red: something is REALLY different. Blue: the differences are minor. Beige: nothing is different; every single byte is the same.
To turn off display of unimportant differences, press the button. The blue will disappear:
If you like these bold colors, you should notice that they look different than yours. In BC you can easily customize your colors . But be warned, until you understand BC and what it is trying to show, you should stick to curated palettes.