Grid row – white spaces appear on mobile

I used a lot of horizontal grid rows in my layouts and color each grid a different color. I don’t use margins, so I get the intended look of seamless grid blocks of color with no whitespace in between. However, when viewed on any kind of mobile device where these horizontal blocks of color have to stack vertically, the result is sizeable white margins between them. It doesn’t seem to matter what I select under screen options. How can I control this behavior and eliminate the margins?