Why does the sky look blue but the sun looks reddish at sunset?

Yes, both are caused by the scattering of sunlight by tiny molecules in the atmosphere. Blue light has a shorter wavelength and is scattered much more strongly than red light. During the day, sunlight passes through a relatively thin layer of air, and the scattered blue light reaches your eyes from all directions, so the sky looks blue. At sunset the sun is near the horizon, so its light travels through a much thicker layer of atmosphere. Along this long path almost all the blue light is scattered away before it reaches you, leaving mostly the longer-wavelength red and orange light to pass straight through. That is why the rising or setting sun appears reddish. The physics, called scattering, is the same in both cases.