The following two sunset pictures are both accurate for color, and are to the same scale.
The first is a familiar sunset on Earth...
Our thick atmosphere causes the orange colors, and causes the Sun to appear squashed a bit.
The next picture is a sunset on Mars...
Mars' thin CO2 atmosphere with iron oxide dust causes the cool blue color at sunset. The atmosphere is not thick enough to distort the Sun's shape, so it is perfectly round. It's apparent size (compared to the Earth picture) reflects the fact that Mars is farther away from the Sun.
