I've seen that before, but always? No. I really wouldn't call that being invisible. Light gray is the color that separates the blocks for individual measures, so when that color is used for the track color as well the whole track ends up looking like one long gray horizontal bar instead of individual blocks for each measure. Even so, the large black dot will still appear in the current measure when the tab is playing.
I wouldn't consider that a big deal. I change the color of most of the tracks on any tab I download anyway because I don't like the default colors (like yellow for bass), or because the person who created the tab used colors I don't like.