not only shade and blue. background scale, menu/windows scale, as well as other UI elements. it no use if menus will become tiny. there's no fun of pixel-hunting to push some button.
btw, doubling resolution of globe shade will make fps drop 4 times (at least). x4 (1280x800) will make fps drop 16 times. it it was 200, it will become 12. and it's quite unplayable. in order to keep mouse responsive, it will require for rendering pipeline refactoring. this is task noone help you. and this task cannot be completed "partly". and i'm affraid any SOFTWARE HD will be unplayable, so it won't work unless engine will be hardware-accelerated (opengl for example). but it will introduce other problems, battlescape shading for example.