Blue color is popping out under my page

Hello! Is there a method to modify the persistent blue default color that appears beneath my background color? This issue is most noticeable on mobile devices. Additionally, can I restrict the screen's movement horizontally, allowing only vertical scrolling? On mobile devices, I encounter this blue color wherever I navigate on the site, and it permits me to go beyond it. On desktop, I observe it both at the top and bottom (below the footer and above the header).
Can I lock it so this color doesn't not appear because it wouldn't let me navigate to that void or can I at least change the color?
Thank you.