How to emphasize a faint white line among a yellow background?
A screenshot is a still image, so you would need to use image-editing software like Photoshop to enhance the image. I recommend messing around in the "Edit > Adjust" menu.  You may be able to show off your effect by increasing the Contrast of the image, or by changing the Hue of the image.  You could probably also replace the yellow color with a different color (though Hue would produce a similar effect).