Why does earth look blue-green when viewed from the space?
Due to reflection of light from water and landmass on its surface
The Earth appears blue-green because it reflects mostly blue/ green colored light rays of the incident sunlight. The sun rays are reflected from water and other landmasses on it's surface.
It appears blue because the oceans reflect blue light, and they cover most of its surface. It appears green in some areas because plantlife covers much of the land area, and plants reflect green light. It appears white as well, because parts of it's surface are covered in snow and ice, and because of large cloud formations.